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Flashcards in Biology 11 Genetics Deck (76):
1

Heredity

passing of traits from parents to their offspring
• Characteristics are passed on by the genes carried on chromosomes
• Dominant and recessive genes →based on allele
o Dominant: expressed
o Recessive: loses out to a dominant gene and stays dormant

2

Genetic Material

DNA: double helix carrying hereditary information

Chromatin: DNA is unwound into chromatin

Chromosomes: Chromatin is condensed into chromosomes

3

DNA

DNA: Deoxyribonucleic (dee-ox-ee-rye-boe-nu-clay-ic) acid

a material found in the cell nucleus that contains genetic information (genes). Chromosomes are made of DNA (genetic information is contained in chromosomes as DNA).
• DNA is very long, but tightly packed into small nucleus due to organization by proteins

4

Chromosomes

o Contained in nucleus of all eukaryotic cells

Structure:
o X shaped (duplicated) ; unduplicated is one strand
o Centromere holds two sister chromatids together
o Vary widely in shape, size, number. In multicellular organisms, chromosomes exist in sets:
•Diploid cells: having two of each type of chromosome (two sets) -->Typically from each parent 2n
•Haploid cells: having only one set of chromosomes n
•Polypoid cells: having more than three sets of chromosomes 3n

o Sex chromosomes: X and Y (XX= female, XY= male)

Chromosome #:
Humans: 46 chromosomes →Diploid (have 23 sets/pairs)
• 22 pairs of autosomes -->Somatic Cells
• 1 pair of sex chromosomes -->sex cells, M or F

5

Gene

•Gene: portion of DNA carrying information that helps produce particular traits of an organism →involved in protein production
o Are chemical instructions to make particular proteins
o Small sets of genes control features such as hair colour and body processes
o Each body cell carries identical sets of genes except for egg and sperm cells (haploid)
o Locus/loci of genes: location of genes on the chromosome (genes for the same feature appear in the same locus on each matching pair of chromosomes)
o Allele: form of gene
• Ex: gene for eye colour has several alleles (blue and brown eyes)

6

Modes of Reproduction (cells)

Asexual:
• A single parent by cell division produces two daughter cells (receive one COPY of each chromosome) that are IDENTICAL to parent and each other (replication)

Sexual:
• Fusion of two sex cells (sperm and egg typically from two different organisms) that produces offspring (not genetically identical)
• Offspring has genes from both parents

7

Cell cycle

Interphase (majority of time), mitosis and cytoplasmic division.

(First nucleus division then cytoplasm division)

8

Before cell division, cells must...

replicate their DNA/genetic information

DNA replication: the process by which DNA is copied, creating sister chromatids joined at the centromere. During this process, each chromosome is copied to produce two sister chromatids (from one single chromosome into two/X→still 23 pairs and still 46 chromosomes, but have 92 chromatids)

9

Mitosis

Mitosis: stage of the cell cycle where the duplicated genetic material of an eukaryotic cell’s nucleus divide equally into two identical nuclei. Mitosis is the division of one nucleus into two identical nuclei.

•Increases cell number during development and replaces damaged or dead cells later in life

10

Phases of Mitosis

PMAT

Prophase, metaphase, anaphase, telophase

In short:
Prophase-chromatin condenses into chromosomes, nuclear membranes disappear, centrosomes move to opposite poles of cell

Metaphase: chromosomes align at metaphase plate, spindle fibres present

Anaphase: spindle fibres retract, separating the sister chromatids to each pole

Telophase: nuclear membrane reforms, cleavage furrow forms, nucleolus forms

11

Interphase

Interphase: most cells spend the majority of there time in interphase. There are 3 phases in interphase: G1 (gap), S (synthesis), G2. In G1, the cell grows, matures and performs normal functions. In S phase, the DNA is copied/replicated. Finally, G2 is where the cell is prepared and ready for division.
• Chromatin (mixture of chromosomes; unwound form of DNA) is formed

12

Prophase

Prophase: (pro = before) the phase of mitosis in which sister chromatids condense and the chromosomes become visible
• Chromatin inside the nucleus condenses (becomes thick) into chromosomes
o Chromosomes are visible under a light microscope
• Centrosomes (two centrioles) move to opposite poles of the cell
o Centrosomes are duplicated before prophase so that each pole has two centrioles (during interphase)
• Nuclear membrane breaks down and the nucleolus disappears
• Extending from the centrosomes are thread-like tubules (part of the cytoskeleton) that begin to form spindle fibres. They continue to extend towards the centromeres on each chromosome.

13

Metaphase

Metaphase: (meta = mid) the phase of mitosis in which the chromosomes are aligned across the centre of the cell
• The longest phase in mitosis
• Spindle fibres extend from the centrosomes/centrioles and attach to each centromere on the chromosome
• Spindle fibres cause chromosomes move and align in the equator of the cell →Metaphase Plate

14

Anaphase

Anaphase: (ana = back) the phase of mitosis in which the centromere splits apart and the sister chromatids are pulled to opposite sides of the cell by the spindle fibres (caused by retracting of spindle fibres by centrioles)

• One of the shortest phases in mitosis, anaphase is when the protein in the centromere break apart thus separating the two chromatids and making two chromosomes.
• The spindle fibres stretch between the chromosomes at the middle of the cell and the centrosomes located on opposite ends. The spindle fibres then retract and separate the sister chromatids of each duplicated chromosome by pulling a chromatid to each end of the cell (chromatid then becomes chromosome)

15

Telophase

Telophase: (Telo = end) the phase of mitosis in which two daughter nuclei are formed
• Nuclear membrane begins to reform around the two new daughter nuclei. Cell membrane pinches forward to create cleavage furrow (in animal cells is the indentation where cytoplasmic division will occur)→causes original cell to divide into two daughter cells. In each nucleus, a nucleolus forms as well. The chromosomes become less coiled and more difficult to see.
• Mitosis is complete and the cell is ready to divide.
• *Chromosomes become DNA

16

Cytokinesis

Following mitosis, the division of the cytoplasm, separating the two nuclei and cell contents into two daughter cells

17

Cloning

the process of creating identical genetic copies/offspring of an organism, single cell or tissue.

• Asexual reproduction
• Form of biotechnology→ethics (right or not)
Ex: Plant Cloning:
o Used commercially
o Orchids, bananas, grapes, petunias
o Not all plants clone well Ex: legumes, grass
o Inexpensive
o GMO: genetically modified organisms
• DNA has been modified using genetic technology/engineering
• Gene may be altered and reinserted into an individual of the same species or inserted into another organism
• Resistance to diseases

Animal cloning: expensive
o 1996 first mammal cloned: Dolly the Sheep
• 3 adult sheep; two cells (sheep A and sheep B + surrogate mother sheep C)
• 277 attempts (long time)
• Cons of clones: not live as long (more susceptible to health disorders)→Dolly died prematurely due to lung disease

18

GMO

Stands for genetically modified organisms
-cost efficient
-Carry genes from other organisms
-Exhibit characteristics of the other species

Ex: commercial insulin (from specially engineered bacteria and yeast containing human insulin gene)
-Human insulin gene inserted in plants and has been successful

19

Mutation

a change in the DNA of an organism. Mutations in genes change the structure and function of the proteins in the cells. Mutations are caused by mutagens, substances or factors that can cause a mutation in DNA. They damage DNA. Ex: electromagnetic radiation (x rays, uv rays/sun).

20

Types of Cells in the body?

1) Somatic cells: Body Cells

2) Sex Cells: known as Gametes, include egg and sperm
-Haploid (n)
-not body cells
-Sperm: produced in males gonads (testes)
-Egg: known as ovum/ova, produced in female gonads (ovaries)

Germ cells: immature reproductive cell that gives rise to haploid gametes when it divides

Germ cell -->Haploid Sex Cells -->Zygote (fusion of sex cells)

21

Significance of genetic diversity

Genetic diversity results in organisms that are do not consist of the same traits and genes, leading to higher survivability

Ex in cells:
• Crossing Over produces chromosomes that have unique combinations of paternally and maternally derived regions
• Independent assortment allows each daughter cell to receive a random chromosome, making each daughter cell genetically unique
-Random Fertlization:

22

Life process/cycle involving cells

germ cell undergoes meiosis to become gametes (sperm or egg)-->fusion of sperm and ovum makes a diploid zygote-->zygote undergoes mitosis to make more cells-->human

23

Fertilization

Fusion of two gametes to form a zygote (after meiosis and production of gametes)

• During ovulation, an ovum is released from the ovary and transported through fallopian tube to an area where fertilization can occur
• One egg (n) and one sperm (n) fuse to form a zygote (2n): the first cell of a new individual
o Zygote is diploid with 23 chromosomes from maternal parent and 23 chromosomes from paternal parent

Sperm + Ovum (egg) -------------→ Zygote
Haploid + Haploid -----------------→ diploid

24

Homologous Chromosomes

Homologous Chromosomes: pair of chromosomes (maternal and paternal) with the same length, shape, and set of genes (shape and size).

-Humans have 23 homologous chromosomes, 22 pairs of autosomes, 1 pair of sex chromosomes

*These homologous chromosomes have one chromosome from mother, one chromosome from father. The pair both give body life instructions for the SAME THING (but with different alleles)

• All chromosomes are homologous except for sex chromosomes (XX or XY)
• Each Homologous set is made up of 2 Homologues (each chromosome in the set is known as a homologue, therefore 2 homologous make up a set)

Homologous chromosomes come to together to form a tetrad

25

Tetrad (*ask)

Structure formed containing two homologous chromosomes
-4 chromatids
-XX
-Carry genes controlling the same inherited traits
-Each locus (location/position of a gene) is in the same position on homologues-->but different function for each person

26

Sex Chromosomes

• Code for sex of offspring (23rd set)
• XX: female
• XY: male
• *X is larger than Y
• Many sex-linked disorders on X chromosome

27

Meiosis

Process by which germ cells divide to produce gametes with half number of chromosomes (Diploid (2n) cells are reduced to haploid (n) cell)

• Sexual reproduction from diploid to 4 haploid (each with half number of chromosomes of original parent diploid cell) Ex: 46 to 23 in each
• 2 cell divisions (I and II); 1 duplication of chromosomes
• Occurs only in gonads


Processes called:
o Spermatogenesis in males (produces 4 sperm)
o Oogenesis in females (produces ova/eggs) -->1 egg and many polar bodies (excess energy)
• Polar bodies ensure that the egg will have a haploid chromosome number and will get enough metabolic machinery to support early division of the new individual. The resulting ovum will have sufficient amount of nutrients, organelles, cytoplasm and chromosomes (haploid) so that the zygote will be diploid.

28

What would happen is meiosis did not occur?

* If Meiosis did not occur the chromosome number in each new generation would double (tetraploid)…. The offspring would die.

29

Meiosis Interphase I

• S phase-chromosomes replicate (X)
• Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres.
• Centriole pairs also replicate: Organelle that purchases spindle fibres (shoot out and retract)
• No cell division (only preparing for division), still perform regular functions
• Nucleus and Nucleolus visible

30

Phases in Meiosis

PMAT
I and II

I: Cell division that reduces the chromosome number by one-half.
◦ Diploid to haploid

•Chromatin condenses into chromosomes, nuclear membrane breaks down etc. →Homologous chromosomes get together to form tetrad (2 chromosomes; 4 chromatids)→crossing over→line up at metaphase plate and independent assortment occurs→homologous chromosomes pull away →divide into two haploid cells →Sister chromatids in each cell separate →forming unduplicated chromosomes and 4 haploid cells

Major occurrences in meiosis: crossing over and non-conjunction

31

Meiosis Prophase I

 Longest and most complex phase (~90% time spent in prophase I)
 Chromosomes condense (chromatin condense into chromosomes)

Synapsis occurs: homologous chromosomes come together to form a tetrad.
◦ Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids).
◦ Chromosome from mom and dad come next to each other
◦ XX

Crossing Over: segments of non-sister chromatids break and reattach to the other chromatid (chromatid from mom attached to chromatid from dad)-physical exchange. →homologous chromosomes exchange corresponding segments during prophase I of meiosis
◦ Site of cross over: the chiasmata (chiasma)
◦ Creates genetic diversity in offspring’s traits
• Exchange genetic material (random assignment at any gene, any time etc.)

32

Meiosis Metaphase I

• Shortest phase
• Tetrads (XX) align on the metaphase plate
• INDEPENDENT ASSORTMENT OCCURS (RANDOM)
o Each daughter cell receives either a maternally derived homologue or the paternally derived homologue from each chromosome pair

1. Orientation of homologous pair to poles is random (The way the tetrads line up is unpredictable)
2. Variation
3. Formula: 2n = # combinations
*must determine value of n first
• Ex: how many combinations of sperm could a human male produce
o 2n = 46
o n = 23
o 2^23= 8 million combinations

33

Meiosis Anaphase I

Homologous chromosomes separate and move towards the poles
Sister chromatids remain attached at their centromeres

34

Meiosis Telophase I

 Each pole now has haploid (n) set of chromosomes
 Cytokinesis occurs and two haploid daughter cells are formed

At the end of meiosis I
*Chromosomes are still duplicated (sister chromatids still attached to one another)

35

Meiosis II

Meiosis II:
• No Interphase I: no more DNA replication
• Similar to mitosis (but occur in the two haploid cells)
• One centriole at each pole (not two)

36

Meiosis Prophase II

• Same as mitosis: nuclear membrane breaks down, duplicated centrioles pairs move to different poles
• No condensing into chromosomes (already condensed)

37

Meiosis Metaphase II

• Same as mitosis: single chromosomes (not homologous) aligned at metaphase plate, completed formation of spindle fibres

38

Meiosis Anaphase II

• Same as mitosis: sister chromatids separate and move towards each pole. Separated chromatids are now called chromosomes

39

Meiosis Telophase II

• Same as mitosis: Nuclei form around chromatids on either side. Cytokinesis occurs

• Result: 4 haploid daughter cells produced (gametes)-1 to 2 to 4
o Each with haploid set of chromosomes

40

Meiosis Vs. Mitosis

Mitosis:
-asexual reproduction
-Results in two diploid daughter cells (identical)
-For growth and repair
-1 division
-Ex: repair skin cells
-Same number of chromosomes as parent cell

Meiosis:
-Sexual Reproduction (performed by sexually reproducing organisms)
-Results in four haploid cells (not identical)
-For reproductive and sex cells
-Half the number of chromosomes as parent cell
-Cells are from sex organs (ovaries/testes in animals)
-2 divisions

41

Non-disjunction

the failure of homologous chromosomes, or sister chromatids, to separate during meiosis

 Results with the production of zygotes with abnormal chromosome numbers -->damaging to the offspring

Non-Disjunction Types:
-Monosomy: One instead of two chromosomes
-Trisomy: Three instead of two chromosomes
-Disorders based on chromosome set number
◦ Trisomy 21 = three chromosome 21 set ←down syndrome

Non-Disjunction Syndromes
-Down syndrome (extra chromosome in set 21: 47 chromosomes)
• Trisomy 21

-Turner syndrome: One X and no Y chromosome →45 chromosomes
• Affects females, missing X chromosome
• 1: 2500
• Monosomy 23 (X)

-Klinefelter syndrome: Two X and one Y chromosome →47 chromosomes
• Males exhibit feminine body characteristics
• 1: 500
• Trisomy 23 (XXY)

-Patau syndrome: trisomy of chromosome 13
• Affects live births, rare, often leads to other damage and death
• 1: 25 000

-Edwards syndrome: trisomy of chromosome 18
• Many organ system defects, death, rare (not as rare as patau)
• 1: 6000

42

Amniocentesis

A procedure a pregnant woman can have in order to detect some genetics disorders (non-disjunction disorders)
◦ Typically done in women who have children at an older age
- Take sample of amniotic fluid to see fluid composition

43

Karyotypes

Karyotypes: chromosomal picture of a person’s chromosomes
o One way to analyze amniocentesis
o Sex: look at pair 23 (long X short Y)

44

Meaning of following terms:
Genome, Genes, Genotype, Phenotype

Genome: Complete complement of an organism’s DNA (entire set of DNA)

Genes: have specific places on chromosomes (loci)

Genotype: the genetic composition of an organism (ex: PP, Pp, pp)

Phenotype: the physical expression of an organism’s observable traits (Ex: blue eyes, freckles etc.)

45

Meaning of following terms:
Alleles, Homozygous, Heterozygous, Dominant, Recessive

Alleles: variations of a gene
 Represented with letters for different types of alleles (ex: PP, Pp, pp)

Homozygous: pair of identical alleles for a character/gene (PP, pp)

Heterozygous: two different alleles for a gene (Pp)

Dominant Genotype: At least one dominant allele is present (R-)
 Refers to an allele that masks the effect of a recessive allele paired with it (italic capital letter)

Recessive genotype: Both recessive alleles must be present (rr)
 In order to see recessive trait, must be homozygous
 Refers to an allele with an effect that is masked by a dominant allele on the homologous chromosome (italic lowercase letter)

46

Meaning of following terms:
Character, Trait, True-bred, Hybridization

Character: Heritable feature; quantifiable, heritable characteristic (ex: flower colour)

Trait: Variant for a character (ex: white flowers, purple flowers)

True-Bred: All offspring of the same variety (ex: true-bred dogs, no mixing)

Hybridization: Crossing of two different true-bred organisms

47

Who is the father of genetics?

Gregor Mendel:
-An Austrian monk from the 1800s
-Suggested that when crossed, organisms had heritable traits
-Mendel experimented with thousands of pea plants to document traits carried from one generation to the next

Discovered three laws of inheritance:
1. Law of Segregation
2. Law of Dominance
3. Law of Independent Assortment

*Pea Plant naturally self-fertilizing (flowers produce both male and female gametes)

48

Explain Mendel's experiments with pea plants

Examined plants of varying heights (tall or short -->T = tall, t = short) -Seven experiments

•He crossed two parent (P) plants (short x tall) and got ALL tall plants in the F1 generation (dominant over recessive)
•He crossed the F1 plants (crossed offsprings; heterozygous) and found that ¾ were tall in the F2 generation (1/4 short)

•Examined other traits on pea plants (round x wrinkled, yellow x green) and got similar results

Ratio of ~3:1 (for traits) in F2 generation

Mendel concluded that there must be a dominant trait that is always expressed when present, and a recessive trait that is expressed only when the dominant trait is not present (law of Dominance)

49

Explain Mendel's experiments with pea plants

Examined plants of varying heights (tall or short -->T = tall, t = short)
•He crossed two parent (P) plants (short x tall) and got ALL tall plants in the F1 generation (dominant over recessive)
•He crossed the F1 plants (crossed offsprings; heterozygous) and found that ¾ were tall in the F2 generation (1/4 short)

•Examined other traits on pea plants (round x wrinkled, yellow x green) and got similar results

Ratio of ~3:1 (for traits) in F2 generation

Mendel concluded that there must be a dominant trait that is always expressed when present, and a recessive trait that is expressed only when the dominant trait is not present (law of Dominance)

50

What is the examination of one trait called?

Monohybrid

-Single Trait Inheritance
-phenotypic ratio of 3:1 (if heterozygous parents)

Ex: Monohybrid Cross Punnet Square

51

What happens when two identically heterozygous for one gene are crossed? Ex: Aa X Aa

Offspring will have 3:1 ratio

ex: AA, Aa, Aa, aa

52

Mendel's Law of Dominance


•When crossing two parents that are pure for contrasting traits (homozygous), only one form of the trait (dominant expressed) will appear in the F1 generation. The recessive trait will be hidden
• The dominant allele produces the same phenotype in heterozygotes and homozygotes
• Factor that remained hidden in F1 generation but is present in the F2 generation is the “recessive factor”

P generation: both parents homozygous
F1: heterozygous
F2: 3:1 (3 will show dominant trait, 1 will show recessive trait)

53

Mendel's Law of Segregation

The members of each pair of genes (alleles) on homologous chromosomes end up in different gametes (4 different gametes; 4 possible combinations) during meiosis
*The ALLELES of a given locus segregate into separate gametes during meiosis

 Alleles (one from each parent) result in variations in inherited characteristics
 For each character, an organisms inherits two alleles (1 allele per parent)-->normal circumstances
 The alleles for each character segregate/separate during meiosis
 Alleles for a trait are recombined at fertilization ->genotype of offspring

54

Mendel's Law of Independent Assortment

 Alleles for different traits are distributed to sex cells (and offspring) independent of one another

Each member of a pair of genes on homolgous chromosomes tends to be distributed into gametes independently of how other genes are distributed during meiosis

 The alleles of one gene sort into the gametes independently of the alleles of another gene. If two genes are located on different chromosomes, then the segregations of different genes do not affect each other (i.e. penny and dime-penny does not affect results of dime)

 Caused by random assortment of chromosomes during meiosis

*associate with dihybrid cross

55

Punnett Square

diagram used to predict the genetic and phenotypic outcome of a cross. These are useful for predicting inheritance patterns of two or more genes simultaneously

• Sizes vary (monohybrid, dihybrid, trihybrid etc.)
• Place genotype for one organism on one side of the square

56

Laws of Probability

• Take the probability for one event and multiply by the probability of other events to find the probability
• One event DOES NOT INFLUENCE the other event (ex: flipping a coin)

57

Test cross

one can cross an unknown organism with another that is homozygous recessive for the traits in question (an individual has a dominant trait, but does not know the genotype→could be PP or Pp. Therefore, is crossed with an individual known to be homozygous recessive→offspring reveal whether the tested individual is heterozygous or homozygous)

If dominant parent is homozygous..
offspring will all express dominant trait

if dominant parent is heterozygous...
1/2 offspring will be dominant heterozygous and 1/2 offspring will be recessive homozygous

58

Double Inheritance

• When examining two traits, we perform a dihybrid cross (di = two)

o Separate Alleles and place the potential parent gametes side of punnet square (like in meiosis) →only can have one allele in a gamete (not Gg, can have GT because they are separated in meiosis when making gametes)

• Ex: Mendel’s Dihybrid Cross: round yellow x wrinkled green
• Phenotypic ratio (traits ex: tall purple flowers): 9:3:3:1 -->Ratio for when breeding two heterozygous traits (Ex: BbEe X BbEe)

• Instead of parents having one trait, dihybrid have two traits (ex: colour of flower and stem length).

o Parents are homozygous for both dominance and homozygous for both recessive (ex: PPTT and pptt)
o Meiosis in a homozygous individual results in one type of gamete (ex: PT and pt)
o Cross between two homozygous individuals (parents) yields offspring with one possible genotype (ex: F1 = PpTt from punnett square)
o Meiosis in dihybrid individuals results in four kinds of gametes (PT, Pt, pT, pt)

59

Codominance vs. Incomplete Dominance

Codominance and Incomplete dominance are both where the heterozygotes do not look like the homozygotes.

Codominance refers to two alleles that are both fully expressed in heterozygotes and neither is dominant over the other (no dominant, no recessive).
• May occur in multiple allele systems: gene for which three or more alleles persist in a population
o Ex: ABO gene
• Both alleles are expressed in the phenotype
• Alleles are not blended
• Genotype includes a Larger letter with smaller letters
o Ex: IAIB ←both dominant allels
• Ex: Roan cows
o Red and white cow

Incomplete dominance: effect in which one allele is not fully dominant over another, so the heterozygous phenotype is between the two homozygous phenotypes.
• Phenotype shows a blended expression of both alleles with a heterozygous trait (heterozygotes)
• Ex: Snapdragon plants
o RR→red flowers
o rr→white flowers (no pigments due to mutated allele r)
o Rr→ pink
o Result of a cross between two pink-flowered heterozygous plants (Rr) →1:2:1 for red, pink and white

60

During fertilization, which two cells come together?

Mature sperm and secondary oocyte

61

Symbols for pedigree

Square-male
Circle-female
Diamond-sex undesignated
Shaded black-affected with trait
Half black half white-carrier for autosomal trait
circle with dot- carrier for X-linked trait

62

Multiple Alleles for Blood types

 Gene has three possible alleles (IA, IB, i)

◦ Each allele codes for a different enzyme
◦ Enzyme places different sugars on the surface of the RBC

 IAIA (type A): enzyme places on type of sugar on the surface (homozygous for Type A)
 IBIB (type B): different enzyme places a different sugar on the surface (homozygous for type B)
 IAIB (type AB): both sugars are placed on the surface ß CODOMINANCE ßshow both A and B
 ii (type O): lacks the sugars of A, B, AB
 IAi (type A): DOMINANT (heterozygous)
 IBi (type B): DOMINANT (heterozygous)

63

What is Autosomal Inheritance?

Autosomal Inheritance: inheritance of alleles located on autosomal (non-sex) chromosomes

Recall autosome is any chromosome that is not a sex chromosome
• A dominant allele on an autosome is expressed in people who are heterozygous for it as well as those who are homozygous
• Traits tend to appear in every generation and affect BOTH SEXES EQUALLY
o Due to no difference between the autosomes of males and the autosomes of females

64

What is sex-linked inheritance?

Sex-linked Inheritance
• Traits associated with alleles on the X chromosome tend to affect more MEN than women. Men cannot pass such alleles to a son (because pass Y chromosome instead); carrier mothers bridge affected generations
• Some traits are located on sex chromosomes (either X or Y)
• Many sex-linked traits are X-linked, meaning that they are carried on the X chromosome (RECALL: Female = XX, Male = XY)

• Examples of sex-linked disorders: Male-pattern baldness (inherited from mother), haemophilia (X-linked), red-green colour blindness, myopia (eyes and vision)

• Punnett Square:
o Use of X and Y with smaller letters for the trait
• Dominant: capital
• Recessive: lowercase (typically the one with disorder. I.e h for with hemophilia)
o 1) X and Y
o 2) Smaller letters
o 3) regular punnet square

65

What is meant by a carrier?

Carrier: an individual who can carry certain gene/allele for a gene
• Males cannot be carriers because they only have one X and must express the trait (also cannot be heterozygous; Y cannot mask the effects of the allele on the X chromosome)
o Therefore, females tend to be carriers for sex-linked disorders
• Females can be carriers: heterozygous (carrier of both traits; capital and lowercase)
• *If male gets the disorder inherited from mom, will have disorder. Only if the female has two copies of the recessive gene (one on each X chromosome) will she then express the disorder

*typically disorders are recessive, therefore when men inherit the recessive allele on the X chromosome, they must express the allele for they do not have another X chromosome to mask the effects

66

Sex-linked inheritance example: hemophilia

Sex-linked example: Hemophilia
• Mother is carrier →XHXh
• Father does not have hemophilia →XHY
• Offspring: BECAREFUL with gender (daughter vs. son)
o Dominant still masks recessive traits (for females)
o Since males only have one X, must express

*Y-linked is when disorders are passed on from father to son (but fewer due to small size of Y chromosome and reduction in genetic information)

67

Pedigree Charts

Pedigrees: Map of family traits used to understand genetic transmission of a trait through a family (Show how the trait is being passed on)
• Chart of family connections that shows the appearance of a trait through generations

• Symbols are used to describe a person’s characteristics
• Autosomal and sex-linked traits can often be identified through the use of a pedigree chart

o Autosomal: simple letters
• Traits affect both female and male
o Sex-linked: X and Y plus smaller letters
• One gender (male) tends to show trait more than other (not equal)

68

Use of Pedigree Charts?

 Genetic counsellors construct and analyze pedigrees to help trace genotypes and phenotypes within a family
 Can determine if and how a particular trait runs within a family
 Ex. Hemophilia (blood clotting disorder) can be detected in expecting parents to demonstrate the pattern of the allele and likelihood of the child receiving the trait
 Extremely useful for animal and plant breeders
 Can be used to track the inheritance of both desirable and undesirable traits
 Farmers may ask for copy of the pedigree before buying or before breeding
 Race horses may be sold to parents solely based on their pedigrees

69

Tips when working with pedigrees

Tips when interpreting Pedigree Charts:
-identify if showing sex-linked or autosomal inheritance
• If one sex is getting a trait over the over, = most likely sex-linked
-determine which trait is expressed (coloured in; could be dominant or recessive trait depending on disorder)
-determine the genotype and phenotype for each trait (ex: colourblind)
-work way backwards

70

What happens when a homozygous dominant for an allele organism crosses with an organism that is homozygous recessive for an allele?

Result: 100% dominant trait (recessive trait is hidden)
Aa

71

Significance of Meiosis

Without meiosis, the number of chromosomes per cell would double in each generation of offspring, leading to unstable conditions that could threaten the viability of a species.

If egg and sperm were produced by mitosis, the resulting gametes would be diploid instead of haploid, leading to a zygote that would be tetraploid (4n) and with 8 sets.

Meiosis generates genetic diversity by ensuring that the gametes it gives rise to will differ from one another. In this, it is unlike regular cell division, or mitosis, which produces daughter cells that are exact genetic copies of parent cells.

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What are chromosomes formed after crossing over called?

Recombinant chromatids

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Mendel's experiments dominant vs. recessive

Stem Length
-Dom: tall
-Rec: short

Seed Colour
-Dom: Yellow
-Rec: green

Pod texture
-Dom: smooth
-Rec: wrinkled

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Blood Rejection

Blood Rejection:
 If you are infused with incompatible blood, Agglutination occurs
 Agglutination: The antigens in your blood bind to the antibodies of the donor blood and cause the blood to clump

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Sickle cell anemia is an example of...

recessive autosomal disorder

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Common traits

Brown eyes Dom
Blue eyes Rec

Tongue rolling Dom
Non-tongue rolling Rec

Freckles Dom
No freckles Rec