Meiosis and Genetic Inheritance

Question 1

Meiosis

Answer 1

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

Question 2

Process of Meiosis

Answer 2

Two rounds of division called meiosis I and meiosis II

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

Question 3

Meiosis I

Answer 3

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

Known as reduction division

Question 4

Prophase I

Answer 4

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

Crossing over may occur, genetic recombination

Question 5

Crossing Over or Genetic Recombination

Answer 5

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

Question 6

Gene Linkage

Answer 6

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

Question 7

Single Crossover

Answer 7

Chromosomes may exchange sections of genetic information just once

Question 8

Double crossover

Answer 8

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

Question 9

Gene mapping

Answer 9

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

Question 10

Metaphase I

Answer 10

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

Question 11

Anaphase I

Answer 11

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

Question 12

Telophase I

Answer 12

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

Question 13

Polar Body

Answer 13

Produced in female oocytes

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

Question 14

Meiosis II

Answer 14

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

Question 15

Nondisjunction

Answer 15

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

Question 16

How does trisomy 21 happen?

Answer 16

Known as Down syndrome

Caused by nondisjunction of chromosome 21 in Anaphase I

Question 17

Gametogenesis

Answer 17

Production of gametes

Different for males than for females

Question 18

Gametogenesis in Males

Answer 18

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

Question 19

Male gamete

Answer 19

Sperm

Question 20

Gametogenesis in Females

Answer 20

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

Question 21

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

Answer 21

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

Question 22

Genetic Leakage

Answer 22

Flow of genetic information from one species to another

Question 23

Locus

Answer 23

Position on a chromosome

Question 24

Wild type

Answer 24

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

Question 25

Genotype

Answer 25

Individual’s genetic makeup of a certain trait or allele

Question 26

Phenotype

Answer 26

Expression of the trait of an allele

Expressed through the action of enzymes and other structural proteins which are encoded by genes

Question 27

Complete dominance

Answer 27

Dominant allele masks expression of the recessive allele

Mendel’s pea plants, purple vs. white

Question 28

Homozygous

Answer 28

Individual with a genotype having two dominant or two recessive alleles that are the same

Question 29

Heterozygous

Answer 29

Individual with a genotype having one dominant and one recessive allele

AKA hybrid

Question 30

Law of Segregation

Answer 30

Mendel’s first law of Heredity

Alleles segregate independently of each other when forming gametes during meiosis

Question 31

Penetrance

Answer 31

Refers to the probability of a gene or allele being expressed if it is present

Penetrance of dominant allele is 100%

Question 32

Expressivity

Answer 32

Measure of how much the genotype is expressed as a phenotype
Degree of expression
Relevant when considering incomplete dominance (intermediate phenotypes)

Question 33

Incomplete dominance

Answer 33

When a heterozygous individual exhibits a phenotype that is intermediate between its homozygous counterparts

Question 34

Co-dominance

Answer 34

Heterozygous individual exhibits both phenotypes

E.g. Human blood type alleles are co-dominant because a heterozygous individual exhibits A and B antigens

Question 35

Punnett Square

Answer 35

Predicting genotypic ratios of offspring from parent genotypes

Question 36

Law of Independent Assortment

Answer 36

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

Question 37

Dihybrid Cross

Answer 37

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

Question 38

Sex Chromosome

Answer 38

Each partner in the 23rd pair of chromosomes (X or Y)

Y chromosome contains only a few genes

Question 39

Sex-linked trait

Answer 39

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

Question 40

Barr body

Answer 40

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

Question 41

Carrier

Answer 41

Female may have recessive trait on 23rd pair of chromosomes without expressing it
- strong chance of being expressed in male offspring

Question 42

Hardy-Weinburg Equilibrium

Answer 42

Theoretical state of suspended evolution in which there is no net change happening in allelic frequencies over time

Question 43

Hardy-Weinburg equation

Answer 43

p^2 + 2pq + q^2 = 1

Equation predicts genotype frequencies of a gene with only two alleles in a population in Hardy-Weinberg equilibrium

Question 44

Difference between Mendel’s calculations and Hardy-Weinberg equation?

Answer 44

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

Question 45

Gametes

Answer 45

Haploid reproductive cells