genetic processes Flashcards
(106 cards)
1
Q
genetics
A
the study of heredity and variation of living organisms and how genetic information is passed from one generation to the next
2
Q
cell theory
A
- all living things are composed of one or more cells
- cells are the smallest units of living organims
- new cells come only from pre-existing cells by cell divsion
3
Q
somatic cell
A
a plant or animal cell that forms the body of the organism; excludes reproductive cells
4
Q
stages of the cell cycle
A
- interphase is the stage during which a cell carries out its normal functions, grows, and makes copies of its genetic material in preparation for the next stage of the cycle
- mitosis is the stage during which a cell’s nucleus and genetic material DIVIDE
- cytokinesis begins near the end of mitosis and involves the division of the cell cytoplasm and creation of a new cell
5
Q
chromosome
A
a structure in the nucleus that contains DNA
6
Q
sister chromatid
A
one of two chromosomes that are genetically identical and held together at the centromere
7
Q
centromere
A
the region where two sister chromatids are held together in a chromosome
8
Q
spindle fibre
A
a microtubule structure that facilitates the movement of chromosomes within a cell
9
Q
centrosome
A
a structure that helps to form the spindle fibres
10
Q
homologous chromosome
A
a chromosome that contains the same sequence of genes as another chromosome
11
Q
gene
A
a part of a chromosome that governs the expression of a trait and is passed on to offspring: it has a specific DNA sequence
12
Q
allele
A
one of two or more forms of a gene
13
Q
karyotype
A
a photograph of pairs of homologous chromosomes in a cell
14
Q
asexual reproduction
A
reproduction that requires only one parent and produces genetically identical offspring
15
Q
sexual reproduction
A
reproduction that requires two parents and produces genetically distinct offspring
16
Q
gaMETE
A
a male or female reproductive cell; a haploid sex cell (egg or sperm)
17
Q
zygote (shawarma)
A
a diploid cell formed by the fusion of two gametes
g = Reproductive cell of an animal or plant
18
Q
fertilization
A
the joining of male and female haploid gametes
19
Q
haploid
A
describes a cell that contains half the number of chromosomes as the parent cell
20
Q
diploid
A
describes a cell that contains pairs of homologous chromosomes
21
Q
meiosis
A
the cellular process that produces cells containing half the number of chromosomes as the parent cell; the process of cell division that produces haploid sex cells (egg or sperm)
22
Q
synapsis (chakara)
A
the aligning of homologous chromosomes during prophase I in meiosis I
23
Q
non-disjunction
A
the failure of homologous chromosome pairs or sister chromatids to separate during meiosis
24
Q
monosomy
A
the loss of a chromosome as a result of non-disjunction
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trisomy
the gain of an extra chromosome as a result of non-disjunction
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selective breeding
the process of breeding plants and animals for desirable traits
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artificial insemination
the process by which sperm are collected and concentrated before being introduced into the female's reproductive system
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embryo transfer
the process in animals by which an egg that has been fertilized artificially is transferred into a recipient female's uterus.
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in vitro fertilization
the technique used to **fertilize egg cells outside the female's body**
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cloning
a process that produces identical copies of genes, cells, or organisms
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gene cloning
the use of DNA manipulation techniques to **produce multiply copies of a single gene or segment of DNA**
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recombinant DNA
a molecule of DNA that includes genetic material from **different sources**
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therapeutic cloning
the process of **replacing an egg cell's nucleus** with the **nucleus from a SOMATIC DONOR CELL to produce a cell line of genetically identical cells**
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reproductive cloning
the process of producing genetically identical organisms
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stem cell
an undifferentiated cell that can develop and become specialized into different cell types of the bod
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trait
A specific characteristics or feature exhibited by an organism
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TRUE breeding (true jackson vp!)
Organisms that exhibit the **same traits generation after generation**
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cross
The specific fertilization of a male and female gamete of **specific genetic origin**
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P generation
The parent generation the organisms initially crossed
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F1 generation
The offspring(s) of the P generation
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monohybrid cross
A cross of two individuals that differ by one trait
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F2 generation
The offspring of a cross between the F1 generation
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dominant
A trait that always appears when an individual has an allele for it
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recessive
A trait that only appears when two alleles are present for it
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law of segregation
Traits determined by pairs of alleles that **segregate during meiosis so that each gamete receives one allele**
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genotype
The combination of alleles for any given trait or entire genetic make-up
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phenotype
The physical and physiological traits of an organism
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homozygous AA ,aa
Two identical alleles of a gene
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heterozygous Aa
Two different alleles of a gene
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Punnett square
A grid used to illustrate all possible genotypes and phenotypes of offspring from genetic crosses
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test cross
A cross between a **parent of an unknown genotype and a homozygous recessive parent**
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dihybrid cross
A cross of two individuals that differ in two traits due to two different genes
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law of independent assortment
Two alleles for one gene segregate or assort independently of the alleles for other genes during meiosis
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chromosome theory of inheritance
Traits determined by genes are **inherited through the movement of chromosomes during meiosis**
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Pedigree
A flow chart that uses symbols to show the **inheritance patterns of traits in a family over many generations**
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Autosomal inheritance
The inheritance of traits **determined by genes of the autosomal chromosomes 1 to 22 in humans**
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Autosomoal dominant
The inheritance of the dominant phenotype whose genes on the autosomal chromosome
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Autosomal recessive
The inheritance of a recessive phenotype is gene is on the autosomal chromosome
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Genetic counselor
A healthcare professional with specialized training in medical genetics and counseling
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Genetic therapy
A technique and treating genetic disorders by introducing the correct form of the defective gene into a parent's genome
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Incomplete dominance
A condition in which neither allele for gene completely conceals the presence of the other it results in intermediate expression of a trait
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Codominance
The condition in which both alleles for a trait equally expressed in a heterozygous both alleles are dominant
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Heterozygous advantage
advantage
A survival benefit for individuals who inherit two different alleles for the same trait
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Continuous variation
A range of variation in one trait resulting from the activity of many genes
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Polygenetic trait
A trait that is controlled by more than one gene
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Linked genes
genes that are on the same chromosome and that tend to be inherited together
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Sex-linked trait
At rate controlled by genes on the X or Y chromosome
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Bioinformatics
A field of study that deals with using computer technology to create and analyze large databases of information
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Genomics
The study of genomes and the complex interactions of genes that result in phenotype
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Genetic profile
The complete genotype of an individual including various mutations
71
Define meiosis
The reduction division of a diploid cell to produce four haploid daughter cells
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Meiosis is the process by which what cells are made
sex cells (gametes) are made in the reproductive organs
It involves the reduction division of a diploid germline cell into four genetically distinct haploid nuclei
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The process of meiosis consists of two cellular divisions:
- The first meiotic division **separates pairs of homologous chromosomes to halve the chromosome number** (diploid → haploid)
- The second meiotic division **separates sister chromatids** (created by the replication of DNA during interphase)
74
what is meiosis preceded by
- Meiosis is preceded by interphase, during which DNA is replicated (in the S phase) to produce two genetically identical copies
- The two identical DNA molecules are identified as sister chromatids, and are held together by a single centromere
- The sister chromatids are separated during meiosis II, following the separation of homologous chromosomes in meiosis I
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How many cell divisions does meiosis have?
2 cell divisions both of which follow the same stages as mitosis (prophase, metaphase, anaphase, telophase)
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Outline meiosis I
The first meiotic division is a reduction division (diploid → haploid) in which **homologous chromosomes are separated**
(it may be followed by a second growth and prep phase called interkinesis)
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prophase 1
P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs at chiasma
chromosomes line up side by side (synapsis)
centromeres move to the poles of the cell and the spindle apparatus forms
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metaphase 1
M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres). Spindle fibres contract causing the bivalents to align them along the middle of the cell
the pairs of homologous chromosomes line up along the equator of the cell. the spindle fibres attach to the centromere of each homologous chromosome
HC L↑ EQ. SP C-M HC
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anaphase 1
A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
homologues chrmosomse serpaarte and move to oppsotei poles of the cell. single chromosome (made up of two sister chromatids) from each homologous pair moves to each pole of the cell. the chromosome number is reduced from 2n (diploid) to n (haploid)
HC OPS POLES. 2N TO N
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telophase 1
T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
homologous chromosome begin to uncoil and the spindle fibres disappear. nuclear membrane from around each group of homologous chromosomes and two cells form and are haploid cells
HC U-C SP BYEE. HIII HAP
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Outline Meiosis II.
The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I)
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prophase 2
P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
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metaphase 2
M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
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anaphase 2
A-II: Spindle fibres contract and separate the now daughter chromatids, chromatids (now called chromosomes) move to opposite poles
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telophase 2
T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) concurrently to form four haploid daughter cells
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outcome of meiosis
- The final outcome of meiosis is the production of four haploid daughter cells
- These cells may all be genetically distinct if crossing over occurs in prophase I (causes recombination of sister chromatids)
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Identify the main differences between meiosis I and meiosis II
Meiosis I:
-Involves the separation of homologous chromosomes (bivalents / tetrads)
-Is a reduction division (diploid to haploid)
-Promotes genetic variation (crossing over and random assortment)
Meiosis II:
-Involves the separation of sister chromatids
-Is a mitotic division (haploid to haploid)
-Does not promote genetic variation
88
Meiosis vs. Mitosis Disco Pug
think DISCO PUG
Division - Mitosis involves only one cell division, but meiosis requires two cell divisions
Independent assortment - Homologous pairs are randomly separated into separate cells in meiosis, but not mitosis
Synapsis - Homologous pairs form bivalents in meiosis, but not mitosis
Crossing over - Non-sister chromatids of homologous pairs may exchange genetic material in meiosis, but not mitosis
Outcome - Mitosis results in the formation of two daughter cells, while meiosis produces four daughter cells
Ploidy - Daughter cells produced by mitosis are diploid, while daughter cells produced by meiosis are haploid
Use - Mitosis is used to clone body cells, while meiosis is used to generate sex cells (gametes)
Genetics - Cells produced by mitosis are genetically identical (clones), while cells produced by meiosis are genetically distinct
89
Similarities between mitosis and meiosis
- Mitosis and meiosis are two processes by which eukaryotic cells may divide and share several similarities:
- They are both preceded by interphase (which includes DNA replication)
- They both divide according to a common pathway (prophase → metaphase → anaphase → telophase)
- They both split their cells via cytokinesis
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How does meiosis create genetic variation?
- crossing over between non-sister chromatids in prophase I
- random/independent assortment of homologous chromosomes in metaphase I
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Outline how crossing over and independent assortment give rise to infinite genetic variety
Crossing Over:
- Crossing over involves the exchange of genetic material between non-sister chromatids of a bivalent
- Bivalents are connected at points called chiasma during the process of synapsis (during Prophase I)
- It is at these chiasma that recombination occurs
Independent Assortment:
- Bivalents will line up at the cell's equator in a random orientation during Metaphase I
- Meaning there is equal probability of a gamete containing the maternal OR paternal copy for any chromosome pair
- Because human cells have 23 chromosome pairs, there are 2^23 possible chromosome combinations (This equates to over 8 million different gamete combinations)
92
Explain how random gamete fusion promotes variation within a species
- When two haploid gametes fuse, they form a diploid zygote which can grow into a new organism
- Because gamete fusion is random, each successive offspring will be composed of a distinct combination of maternal and paternal chromosomes
- This means every member of a species is unique (promoting biodiversity)
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crossing over
crossing over is the exchange of DNA between non-sister homologous chromatids
-the genetic exchange results in the formation of recombinant chromosomes
-these recombinant chromosomes will possess unique combinations of alleles
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steps of crossing over
In prophase I, homologous chromosomes undergo a process called synapsis, whereby they pair up to form a bivalent (or tetrad)
The homologous chromosomes are held together at points called chiasmata (singular: chiasma)
Crossing over of genetic material between non-sister chromatids can occur at these chiasmata
As a result of this exchange of genetic material, new gene combinations are formed on chromatids (recombination)
Once chiasmata are formed, the homologous chromosomes condense as bivalents and then are separated in meiosis
If crossing over occurs then all four haploid daughter cells will be genetically distinct (sister chromatids are no longer identical)
95
explain process of random/independent assortment
During metaphase I, homologous chromosomes line up at the equator as bivalents in one of two arrangements:
-Maternal copy left / paternal copy right OR paternal copy left / maternal copy right
This orientation of pairs of homologous chromosomes is random, as is the subsequent assortment of chromosomes into gametes
The final gametes will differ depending on whether they got the maternal or paternal copy of a chromosome following anaphase I
As this random assortment will occur for each homologous pair, the number of possible gamete combinations are dependent on the number of homologous pairs
-Gamete combinations = 2n (where n represents the haploid number)
96
If chromosome number was not halved in gametes what would happen
total chromosome numbers would double each generation (polyploidy)
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Non-disjunction
refers to the chromosomes failing to separate correctly, resulting in gametes with one extra, or one missing, chromosome (aneuploidy
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The failure of chromosomes to separate may occur via:
Failure of homologous to separate in Anaphase I (resulting in four affected daughter cells)
Failure of sister chromatids to separate in Anaphase II (resulting in only two daughter cells being affected)
If a gamete with one extra chromosome fuses with a normal gamete, the offspring will have trisomy
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Down Syndrome
Individuals with Down syndrome have three copies of chromosome 21 (trisomy 21)
- One of the parental gametes had two copies of chromosome 21 as a result of non-disjunction
- The other parental gamete was normal and had a single copy of chromosome 21
- When the two gametes fused during fertilisation, the resulting zygote had three copies of chromosome 21
100
is there a correlation between maternal age and increased non-disjunction
Yes
The risk of chromosomal abnormalities in offspring increase significantly after a maternal age of 30
There is a higher incidence of chromosomal errors in offspring as a result of non-disjunction in meiosis I
Mean maternal age is increasing, leading to an increase in the number of Down syndrome offspring
reasons: young eggs tend to be less exposed to mutagens and carcinogens - tend to be "healthier"
101
can karyotyping be used to identify non-disjunction events/test for chromosomal abnormalities
yes
cells are harvested from a fetus and induced to undergo division (condenses DNA to make it visible under microscopic conditions)
chromosomes are then stained and photographed to produce a karyogram
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different fetal cell harvesting techniques
Chorionic villi sampling
Amniocentesis
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Chorionic villi sampling
Chorionic villi sampling involves removing a sample of the placental tissue via a tube inserted through the cervix
It can be done earlier at ~11 weeks of pregnancy with a slightly higher risk of inducing miscarriage (~1%)
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Amniocentesis
Amniocentesis involves the extraction of a small amount of amniotic fluid (contains fetal cells) with a needle
It is usually conducted later than CVS (~16 weeks of pregnancy) with a slightly lower risk of miscarriage (~0.5%)
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Differentiate between homologous chromosomes and sister chromatids
- Homologous chromosomes are the maternal and paternal copies of a given chromosomes
- Homologous chromosomes have the same structure and the same genes at the same loci positions
- Sister chromatids are the duplicated copies of the chromosome's DNA (copied during S phase of interphase)
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practice test q: how many codons are there
4 nucleotides - 4x4x4 = 4 ^3 = 64 possible codons
imagine if there were 5 possible nucleotides - 5x5x5 = 5 ^ 3 = 125 possible codons
