Genetics

Question 1

Chromosomes

Answer 1

complex of DNA w/ histone protein
Visible in a dividing cell.
# of chromosomes is constant for a species
Humans 46 (22 pairs of autosomes and 1 pr of sex) in each somatic cell
Not all chromatin is equally active; some genes are active in only certain cells or certain phases of life

Question 2

Sex & autosome chromosomes

Answer 2

Sex determine sex & sex-linked traits; X & Y chromosomes do not carry same genes
Autosomes determine all other characteristics

Question 3

Homologous chromosomes

Answer 3

pairs of chromosomes, one from each parent; contain similar but not the same genes (alleles) coding for same set of characteristics

Question 4

Haploid (n)

Answer 4

Single set of chromosomes (one member of each homologous pair)

Question 5

gamete

Answer 5

possesses only one haploid (n)

Question 6

Zygote

Answer 6

when two gametes unite in fertilization, it results in two sets of chromosomes or diploid (2n)

Question 7

Human zygote & all somatic cells

Answer 7

2n = 46

Question 8

Gamete

Answer 8

n = 23

Question 9

Mitosis

Answer 9

1. responsible for growth, replacement of damaged somatic cells
2. responsible for producing a multicellular organism from a single-celled zygote

Question 10

Mitosis in asexually reproducing animals

Answer 10

Transfers genetic information from parent to progeny

Question 11

Daughter cells in mitosis

Answer 11

Each one is ID to parent cell but can later differentiate by differential gene expression

Question 12

Cell division by mitosis

Answer 12

consists of a division of nuclear chromosomes (mitosis) followed by the division of cytoplasm (cytokinesis)

Question 13

Cell cycle

Answer 13

Interphase
Prophase
Metaphase
Anaphase
Telophase

Question 14

Prophase

Answer 14

1. Nuclear envelope disintegrates
2. Centrosomes replicate; two centrioles migrate to opposite poles of cell
3. Microtubules join centrioles to form spindle
4. Chromatin condenses into chromosomes: each has 2 id sister chomatids (formed by DNA replication) joined at their centromere

Question 15

Metaphase

Answer 15

Chromosomes line up in the middle of the nucleus

Question 16

Anaphase

Answer 16

Sister Chromatids seperate at the centromere and move to opposite poles of nucleus, pulled by centrioles. Each pole now has complete set of chromosomes

Question 17

Telophase

Answer 17

Spindle disappears and chromosomes diffuse into chromatin. Nuclear envelope reappears.

Question 18

Cell division via Meiosis

Answer 18

1. Unlike mitosis, daughter cells are not genetically id to each other or to parent cell.
2. Sexual reproduction requires genetic contribution from two sex cells (gametes), which unite & form zygote
3. To maintain # of chromosomes constant in next generation, the gametes must have 1/2 # of chromosomes as somatic cells

Question 19

gene

Answer 19

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.

Question 20

Meiosis I

Answer 20

1. Similar to mitosis, each chromosome replicates & has 2 chromatids, joined at the centromere.
2. Four chromatids of homologous pair come into synapsis (side by side contact), permitting crossing over (genetic recombination) between nonsister chromatids
3. Unlike mitosis, centromere does not divide. One entire chromosome (that has 2 chromatids) from each homologous pair, is pulled into each daughter cell.
4. At end of Meiosis I, each of 2 daughter cells contains one chromosome of each homologous pair (therefore haploid) but as each chromosome still contains the two chromatids, each cell has twice the amount of DNA.

Question 21

Homologous chromosomes break and . . .

Answer 21

exchange genes; increasing the amt of genetic variation.

Recombination frequency of two loci is directly proportional to the distance between them.

Question 22

Meiosis II

Answer 22

1. The second meiotic division resembles mitosis.
2. Sister chromatids separate at anaphase
3. Each daughter cell now haploid & has normal amt of DNA
4. Four haploid cells formed from 1 diploid cell as result of meiosis. Each cell has only one copy of each chromosome (one copy of each gene).

Question 23

Mendel’s 2 Laws of Inheritance: #1:LAW OF SEGREGATION

Answer 23

1. Law of Segregation: gametes form, paired chromosomes (& genes) specifying alternative phenotypes separate; each gamete receives onluy one of two alternative copies of genes (alleles).
   When paired alleles are alike in the two homologous chromosomes, the individual is a homozygote; if unlike, heterozygote
   Allele expressed in heterozygote is dominant and the allele that is not is recessive
   SHOWS THAT THERE IS NO BLENDING OF TRAITS BECAUSE NONE OF PROGENY HAS AN INTERMEDIATE CHARACTER BUT RATHER HAS ONLY ONE OF THE TWO POSSIBLE CHARACTERS.

Question 24

2: LAW OF INDEPENDENT ASSORTMENT

Answer 24

Genes located on different pairs of homologous chromosomes assort independently during meiosis.

Question 25

Mono- & di-hybrid cross/ratios to demonstrate Mendel's laws

Answer 25

MUST LOOK AT SLIDES

Question 26

Molecular basis of inheritance

Answer 26

The dominant allele codes for a functional protein; the recessive allele codes for a non-functional one.

Question 27

Deviations from Mendel's Laws

Answer 27

1. Not all traits are inherited by simple Mendelian laws. 2. Mendel avoided traits that were inherited under different rules. 3. Numerous factors can cause traits to be inherited in ways that differ from simple Mendelian genetics.

Question 28

Deviation #1: Incomplete dominance or codominance

Answer 28

Both alleles are expressed equally (produce functional proteins) & the heterogynous phenotype is intermediate-a blending of the two parental types. ie ABO blood types

Question 29

Deviation #2: Polygenic or quantitative inheritance

Answer 29

Multiple genes affect a single characteristic. Polygenic characteristics show continuous variation NOT discrete alternatives ie height, skin color

Question 30

Deviation #3: Sex-linked inheritance

Answer 30

Recessive traits are carried on the X chromosome. For the trait to be expressed: a) in a female, both alleles have to recessive b) in a male, only one recessive is sufficient since the male has only one X chromosome A herterogynous female with one recessive allele is a CARRIER for the allele but is phenotypically normal. Therefore the males outnumber females in expression of the trait.

Question 31

Deviation #4: Linkage

Answer 31

All traits do not assort independently, contrary to Mendel's 2nd Law. All genes and therefore traits present on a single chromosome are LINKED & are inherited together. So there are as many linkage groups as there are chromosome pairs. Linked traits can seperate due to seperation of alleles located on the same chromosome - crossing over or recombination.

Question 32

Sources of Phenotypic Variation

Answer 32

1. Reshuffling of existing genetic diversity due to sexual reproduction and meiosis via: a) independent assortment of chromosomes during meiosis b) Crossing over during meiosis c) fusion of random gametes from both parents 2. New genetic variations via mutations

Question 33

Definition of Mutations

Answer 33

random changes in nucleotide sequence that could produce either beneficial or harmful effects. Occur spontaneously due to base pairing errors during replication.

Question 34

Facts about mutations:

Answer 34

1. Mutation in somatic cells are not important for evolution 2. Most mutations recessive and therefore masked by partner's alleles. A population carries a pool of recessive alleles without being expressed 3. Mutation rates vary at different loci. A long gene is more like to mutate than a short gene. 4. About every 3rd persons carries one new mutation.

Question 35

Chromosomal Aberrations

Answer 35

1. Numerical | 2. Structural

Question 36

1. Numerical Aberrations

Answer 36

Euploidy: addition or deletion of one (aneuploidy) or more (polyploidy) chromosomes.

Question 37

Aneuploidy

Answer 37

caused by failure of chromosomes to seperate during meiosis (nondisjunction). As a result, both chromosomes go to one pole and none to other, producing one gamete having n-1 chromosome and other with n+1 chromosomes

Question 38

Monosomy

Answer 38

Result of a n-1 gamete fusing with a normal n gamete. Survival is rare due to lack of genetic instructions.

Question 39

Trisomy

Answer 39

Result of an n+1 gamete fusing with a normal n gamete. ie Downs syndrome (appears > with increasing age of mother but not father)

Question 40

FAct re: seperation during meiosis or disjunction

Answer 40

Since a cell only requires 1 functional X chromosome, non-disjunction of X chromosome is better tolerated but still leads to abnormalities

Question 41

XXY

Answer 41

Klinefelter Syndrome: phenotypically male

Question 42

X (and no Y)

Answer 42

Turner Syndrome: phenotypicaly female.