Meiosis and Genetic Inheritance Flashcards

1
Q

Meiosis

A

Form of cell division that creates gametes that are suitable to be paired sexually with another gamete to contribute genetic information to the next generation

Germ cells undergo two rounds of nuclear division to produce four haploid daughter cells called gametes- unique genetic makeup

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2
Q

Process of Meiosis

A

Two rounds of division called meiosis I and meiosis II

Each consists of successive stages of prophase, metaphase, anaphase, and telophase

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3
Q

Meiosis I

A

Separate homologous chromosomes to produce two haploid cells, each with one copy of the 23 chromosomes

Known as reduction division

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4
Q

Prophase I

A

Homologous chromosomes line up alongside each other, matching genes exactly
Have four chromatids in homologous pair, called tetrads

Crossing over may occur, genetic recombination

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5
Q

Crossing Over or Genetic Recombination

A

Chromosomes “zip” along each other where nucleotides are exchanged forming the synaptonemal complex
- creates ‘X’ shape or chiasma under microscope

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6
Q

Gene Linkage

A

Where genes are physically located near one another, increasing probability that traits will be inherited together despite crossing over

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7
Q

Single Crossover

A

Chromosomes may exchange sections of genetic information just once

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8
Q

Double crossover

A

Chromosomes trade a segment once and then trade back a sub-section of segment
Each chromosome retains some of own original genetic material

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9
Q

Gene mapping

A

A technique which helps determine locations and relative distances of genes on chromosomes

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10
Q

Metaphase I

A

Two homologues remain attached and move to the metaphase plate
- Tetrads align along the plate with 23 tetrads in single file line in humans

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11
Q

Anaphase I

A

Homologous chromosomes each separate from their partner independently assorting to create two haploid cells

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12
Q

Telophase I

A

Nuclear membrane may reform, cytokinesis may occur
- these both occur in humans

New germ cells are haploid with 23 replicated chromosomes and are called secondary spermatocytes or secondary oocytes

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13
Q

Polar Body

A

Produced in female oocytes

One of the germ cells formed after telophase I becomes a polar body, has much less cytoplasm, and degenerates

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14
Q

Meiosis II

A

Proceeds through Prophase II, Metaphase II, Anaphase II, and Telophase II much like mitosis under light microscope

Final products are haploid gametes, each with 23 chromosomes
Four spermatocytes formed
One ovum is formed

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15
Q

Nondisjunction

A

During Anaphase I or II, if any chromosome does not split
Anaphase I: One cell has two extra chromatids and other is missing a chromosome
Anaphase II: Results in one cell having one extra chromatid and one cell lacking a chromatid

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16
Q

How does trisomy 21 happen?

A

Known as Down syndrome

Caused by nondisjunction of chromosome 21 in Anaphase I

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17
Q

Gametogenesis

A

Production of gametes

Different for males than for females

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18
Q

Gametogenesis in Males

A

Diploid progenitor cells called spermatogonia.
Spermatogonium undergoes mitosis to produce two diploid primary spermatocytes
Primary spermatocytes undergo meiosis I to become haploid secondary spermatocytes
Secondary spermatocytes undergo meiosis II to become spermatids
Spermatid loses cytoplasm and gains tail- sperm

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19
Q

Male gamete

20
Q

Gametogenesis in Females

A

Diploid progenitor cell is oogonium
Oogonium undergoes mitosis to produce two primary oocytes before female is born
At puberty, primary oocytes undergo meiosis I, making haploid secondary oocyte
Secondary oocyte arrested at metaphase II until penetrated by sperm (fertilization), complete meiosis II to form ootid, mature into ovum

21
Q

Why does the female oocyte need to conserve cytoplasm by releasing polar bodies?

A

Once an ovum is fertilized, resulting zygote needs to undergo many rounds of division before it is able to implant on the uterine wall and establish a blood supply
Increased cytoplasm present in ovum provides nutrients necessary to sustain a zygote as it becomes a bastula and travels from fallopian tube to uterus

22
Q

Genetic Leakage

A

Flow of genetic information from one species to another

23
Q

Locus

A

Position on a chromosome

24
Q

Wild type

A

Normal or most common allele type for a certain trait within a population

25
Genotype
Individual’s genetic makeup of a certain trait or allele
26
Phenotype
Expression of the trait of an allele Expressed through the action of enzymes and other structural proteins which are encoded by genes
27
Complete dominance
Dominant allele masks expression of the recessive allele | Mendel’s pea plants, purple vs. white
28
Homozygous
Individual with a genotype having two dominant or two recessive alleles that are the same
29
Heterozygous
Individual with a genotype having one dominant and one recessive allele AKA hybrid
30
Law of Segregation
Mendel’s first law of Heredity Alleles segregate independently of each other when forming gametes during meiosis
31
Penetrance
Refers to the probability of a gene or allele being expressed if it is present Penetrance of dominant allele is 100%
32
Expressivity
Measure of how much the genotype is expressed as a phenotype Degree of expression Relevant when considering incomplete dominance (intermediate phenotypes)
33
Incomplete dominance
When a heterozygous individual exhibits a phenotype that is intermediate between its homozygous counterparts
34
Co-dominance
Heterozygous individual exhibits both phenotypes E.g. Human blood type alleles are co-dominant because a heterozygous individual exhibits A and B antigens
35
Punnett Square
Predicting genotypic ratios of offspring from parent genotypes
36
Law of Independent Assortment
Mendel’s Second Law of Heredity Genes located on separate chromosomes assort independently of each other For example, genes that code for distinct traits when located on separate chromosomes do not affect each other during gamete formation
37
Dihybrid Cross
Cross that can be demonstrated on a Punnett square for two distinct traits with a dominant and recessive allele for each in which we cross all possible heterozygous combinations with one another (WG, Wg, wG, wg) x (WG, Wg, wG, wg) Phenotypic ratio: 9:3:3:1
38
Sex Chromosome
Each partner in the 23rd pair of chromosomes (X or Y) Y chromosome contains only a few genes
39
Sex-linked trait
Genes located on the sex chromosomes (usually the X chromosome, because the Y chromosome has very few genes) In males sex-linked genes on X chromosome are expressed whether dominant or recessive
40
Barr body
Most somatic cells have one of the X chromosomes in a female randomly condense to forma tiny dark object Formed at random, so active allele is split approximately evenly among all cells - recessive allele usually still only displayed in homozygous individual
41
Carrier
Female may have recessive trait on 23rd pair of chromosomes without expressing it - strong chance of being expressed in male offspring
42
Hardy-Weinburg Equilibrium
Theoretical state of suspended evolution in which there is no net change happening in allelic frequencies over time
43
Hardy-Weinburg equation
p^2 + 2pq + q^2 = 1 | Equation predicts genotype frequencies of a gene with only two alleles in a population in Hardy-Weinberg equilibrium
44
Difference between Mendel’s calculations and Hardy-Weinberg equation?
Rather than having a 1 in 2 chance of inheriting an allele (A or a) from one of the two parents, here the probability corresponds to the proportion of that allele (A or a) in entire population
45
Gametes
Haploid reproductive cells