W10-Sex Determination

Define sexual dimorphism

The condition where males and females of the same species exhibit different physical characteristics beyond their reproductive organs, such as differences in size, weight, coloration, or behavior.

Sex chromosomes

Pair of chromosomes that determine the sex of the individual

In humans, how many pairs of autosomes are there

22 pairs of autosomes

In humans, how many pairs of sex chromosomes are there?

2 sex chromosomes

Define homogametic sex and give example

Individuals who possess two similar sex chromosomes.

Ex: Females who have 2 X chromosomes

Define heterogametic sex and give example

Individuals who possess two similar sex chromosomes.

Ex: Males who have one X and one Y chromosome

SLIDE 9 and 10

Sex linked

Genes that are located on the sex chromosome

SLIDE 11

In fruit flies, how many pairs of autosomes and sex chromosomes are there?

• 3 pairs of autosomes

  • a pair of sex chromosomes

In fruit flies, how many total chromosomes are present?

8 chromosomes in total

True or False: Fruit flies also have the XY system, similar to humans

True

In female fruit flies, what are the sex pair chromosomes found?

XX

In male fruit flies, what are the sex pair chromosomes found?

XY

What were the advantages to use fruit flies as a genetic model organism?

• Readily available

• Short life cycle

• Simple to culture

• Simple to cross

• Very prolific (can produce large number of offspring)

• Have 4 pairs of chromosomes

• Sexually dimorphic

Y-linked

Gene located on the Y chromosome

X-linked

Gene located on the X chromosome

How is a sex-linked allele denoted for male and female?

• Female: X^NX^N

• Male: X^Ny

Gene N is always located on the X chromosome

What is a wild-type? Give an Ex

The phenotype for a character that is in the natural population

Ex: Fruit flies with red eyes are a wild type

What is a mutant phenotypes? Give an Ex

Alternates tot he wild types, thus phenotypes that are not normally found in the population

Ex: Fruit flies with white eyes

If P generation, red-eyed female X white-eyed male were crossed, what is the F₁ generation?

		Sperm from P (Xry) fruit fly
Eggs from P (XRXR) fruit fly		Xr	y
	XR	XRXr	XRy
	XR	XRXr	XRy

Red is 100% for male and female

If F₁ generation, heterozygous red-eyed female X red-eyed male were crossed, what is the phenotypic ratio of the  F₂ generation and sex specificity?

		Sperm from F1 (XRy) fruit fly
Eggs from F1 (XRXr) fruit fly		XR	y
	XR	XRXR	XRy
	Xr	XRXr	Xry

3 red eyes: 1 white eye

No female had white eyes

What are the gametes produced if a red-eyed female X a white-eyes male crossed (p gen)?

• Red-eyed female is X^RX^R → Gametes → Eggs X^R

• White-eyed male is X^ry → Gametes → Sperm X^r or y

How can one determine whether a gen is located on an autosome or sex chromosome?

By carrying out Reciprocal Cross

Define Reciprocal cross

Refers to when two crosses are done, each with the same phenotypes, but with opposite sexes having the phenotype

Example of reciprocal cross

Red-eyed female X white-eyed male

Red-eyed male X white-eyed female

If the same result occurs when a reciprocal cross is done, is it autosomal or sex-linked?

Autosomal

If different results occur when a reciprocal cross is done, is it autosomal or sex-linked?

sex-linked or sex-chromosome