Non-Mendelian Part 1

What are the RULES OF MENDELIAN INHERITANCE PATTERNS

RULES OF MENDELIAN INHERITANCE PATTERNS
1. The expression of genes in offspring directly influence their traits.
2. Genes are passed unaltered from generation to generation except in rare mutations.
3. Genes obey Mendel's law of segregation
4. In crosses involving two or more genes, genes obey Mendel's law of independent assortment.

Genotype of the mother directly determines the phenotype of the offspring

Maternal Effect

In maternal effect, does Genotype of the father affect the phenotype of the offspring? (Y/N)

No.

Maternal effect are gene products produced by the mother during?

Oocyte Development

first observed maternal effect gene in water snails in the 1920s

Arthur Boycott

Genus name of water snails.

Lymnaea peregra

Observed the pattern of the shell and internal organs (right-handed/dextral or left-handed/sinistral)

Arthur Boycott

In the experiment of Arthur Boycott, what happened in the F1 generation of snails?

F1 Generation:

If a DD female was crossed to a dd male, all F1 offspring were dextral

If a dd female was crossed to a DD male, all F1 offspring were sinistral.

In the experiment of Arthur Boycott, what happened in the F2 generation of snails?

F2 Generation:
F1 mothers are Dd
All dextral snails

In the experiment of Arthur Boycott, what happened in the F3 generation of snails?

F3 Generation:

3:1 ratio (dextral:sinistral)

What rule did Maternal Effect violate?

RULE #1:

The expression of genes in offspring directly influence their traits.

The study of modifications that occur to a gene or chromosome that alters gene expression but is not permanent over the course of many generations.

Epigenetics

Does Epigenetics change DNA sequence, through modifications? (Y/N)

No.

The level of expression of genes on the sex chromosomes is similar in both sexes

Dosage Compensation

Dosage Compensation was coined by?

Herman Muller in 1932 (Drosophila)

One copy of an allele in the female is not equivalent to one copy in the male

Two copies of alleles in the female produces a phenotype similar to that produced by males with one copy

Dosage Compensation

The difference in gene dosage (2 vs 1) is being compensated at the level of gene expression

Dosage Compensation

What are the Mechanisms of Dosage Compensation?

X-chromosome inactivation in mammals

Doubling of X-linked genes in Drosophila

Diminished expression of X- linked genes on both X chromosomes in some hermaphroditic nematodes

proposed that dosage compensation occurs by inactivation of a single X chromosome in females

Mary Lyon (1961)

identified Barr bodies in the somatic cells of female cats but not male cats

Murray Barr, Ewart Bertram

proposed that the Barr body is a highly condensed X chromosome

Susumu Ohno

According to Lyon Hypothesis

Initially both X chromosomes are active. (Y/N)?

Yes.

During ____________, one of the two X chromosomes is randomly inactivated in each somatic cell

embryogenesis

Inactivated X chromosome becomes highly compacted = ?

Barr body

What are the steps in X-Chromosome inactivation?

Nucleation

Spreading

Maintenance

When does Nucleation occur?

Occurs during embryonic development.

The number of X-inactivation centers (Xics) is counted and one of the X chromosomes remains active and the other is targeted for inactivation.

Nucleation

When does Spreading occur?

Occurs during embryonic development.

It begins at the Xic and progresses toward both ends until the entire chromosome is inactivated and becomes a Barr body.

Spreading

When does Maintenance occur?

Occurs from embryonic development through adult life

The inactivated X chromosome is maintained as such during subsequent cell division.

Maintenance