Chapter 19: Sexual Reproduction and Genetics

What are diploid germ-line cells?

They are cells that give rise to haploid gametes by meiosis

What are somatic cells?

They are cells that form the body of an organism and are necessary to support sexual reproduction but cannot produce a progeny of its own

In mitosis, how are duplicated maternal and paternal chromosomes lined up at the metaphase plate?

They are lined up independently at the metaphase plate, with each chromosome consisting of a pair of sister chromatids

In meiosis, how do duplicated maternal and paternal homologs behave during meiosis I and II?

In meiosis, duplicated maternal and paternal homologs pair (synapse) before lining up at the metaphase plate.

• During meiosis I, maternal and paternal homologs separate.

• During meiosis II, the sister chromatids separate.

How are sister chromatids in maternal and paternal homologs held together?

They are held together by the axial core that interacts with the cohesins that hold the sister chromatids together

How does recombination occur?

1. During Meiosis I, protein complexes produce a DSB in the DNA of one of the non-sister chromatids

2. A cross over event then occurs with the undamaged non-sister chromatid, resulting in both chromatids having a segment of DNA from the other

What happens when a crossover event occurs?

A chiasmata, a crossed shaped structure, is formed between the 2 non-sister chromatids

What occurs during metaphase 1?

A chiasmata is created between the maternal and paternal homologs with the cohesin protein keeping the sister chromatids together

How do the kinetochores of sister chromatids function during metaphase I?

They function as a single unit and point toward the same spindle pole

How are homologs pulled apart during anaphase I?

When the cohesin protein holding sister chromatids arms are degraded, it results in the homologs being pulled apart, with the cohesin protein at the centromere remaining intact and keeping the chromatids together while the homologs are pulled to opposite poles

How do the kinetochores of sister chromatids function in metaphase II?

They function independently and point in opposite directions from one another

How are sister chromatids pulled apart during anaphase II?

when the cohesin holding the sister chromatids together at the centromere are degraded, it results in the kinetochores pulling the chromatids toward opposite poles

What happens if there is independent assortment of maternal and paternal homologs during meiosis?

It’ll result in the production of different haploid gametes for an organism with x amount of chromosomes

What happens if there is crossover between maternal and paternal homologs during meiotic prophase?

The DNA segments between the homolog chromosomes are exchanged, leading to 4 different haploid gametes being produced

What happens when nondisjunction occurs during meiosis?

Duplicated maternal and paternal copies fail to separate normally during the first meiotic division, leading to two gametes receiving no copies of the chromosome and two gametes receiving two copies of the chromosome rather than a single copy

What are aneuploid gametes?

Gametes that receive an incorrect # of chromosomes

What if an aneuploid gamete participates in the fertilization process?

It’ll result in the zygote also having an abnormal # of chromosomes, leading to genetic disorders such as down syndrome

What happens when there is a loss-of-function mutation present in a wild-type protein?

It’ll result in either a decrease in protein activity or the elimination of protein activity

What happens when there is a gain-of-function mutation present in a wild-type protein?

It’ll result in either a boost in protein activity or an increase in the amount of wild type proteins present

Why is loss of function mainly recessive?

1. When a person has a single functional and nonfunctional copy of a gene, the functional copy is able to compensate for the loss of function in the mutated copy and mask the effects of the loss-of-function allele

2. But, when a person has two nonfunctional copies of a gene, it’d result in a homozygous recessive state and lead to the manifestation of a disease or phenotype associated with the mutation

However, it can sometimes be dominant as well when haploinsufficiency occurs

Where are SNPs usuaully located near?

Near the gene that causes the disease on the same chromosome