Question

1. State whether the following are true or false:

a. Y-linked traits are phenotypes only seen in males: TRUE/FALSE

b. Y-linked traits can skip generations in pedigrees: TRUE/FALSE

c. Recessive X-linked traits are observed with equal frequency in males and females: TRUE/FALSE

d. Red-green color-blindness is an X-linked recessive trait. Two color-blind parents can have a son with normal vision: TRUE/FALSE

e. Two color-blind parents can have a daughter with normal vision: TRUE/FALSE

f. Two parents with normal vision can have a color blind son: TRUE/FALSE

g. Two parents with normal vision can have a color blind daughter: TRUE/FALSE

h. Males can be carriers for X-linked traits: TRUE/FALSE

2. Can a gene required for mitosis (e.g. tubulin) be located on the Y- chromosome? on the X- chromosome? Why or why not?

Answer 1

Answer -

A- true .

( Males carry XY Chromosomes and females carry XX Chromosomes, so traits linked to Y Chromosome are only inherited by males .)

B- false

Y linked traits are dominant since there is only one Y chromsome in males , dominant traits do not skip generations , only recessive do.

C- false

Revessive X linked traits are expressed more frequently in males than females . Because femalrs carry XX Chromosomes , and to be affected females must carry the allele for the trait on both X chromosome . If present only on one X chromosome the female appears normal amd is a carrier. But since males are XY , one copy of the allele on X is enough for expression of the trait.

D- false.

Lets say * is the allele for colorblindness .

So color blind mother = X* X*

Colour blind father = X* Y

F1-

	X*	Y
X*	X*X*	X*Y
X*	X*X*	X*Y

100% all offsprings - son / daughter will be colorblind of both parents are affected.

E- false

Same answer as question D.

F- false.

Parents are both normal vision ,

Let * be allele for colorblindness.

So mother XX

Father. XY

	X	Y
X	XX	XY
X	XX	XY

Since both parents do not carry * ( color blindness) allele , all children will be normal - 100%.

G- false

Same answer as F

h- false.

Only females are carriers in x linked recessive traits . Males are never carriers . Females are carriers when one X carries a copy of defective allele and another X carries a normal allele .

So lets say in case of colorblindness = X* X'

(Where * is allele for colorblindness and ' is allele for normal vision ) .

In this case the female will be normal with normal vision as dominant allele suptesses the color blindness allele. But males are XY , so one fopy of the allele on X is enough for colorblindness . Cannit have a carrier state.

2. No . X and Y chromsomes are present in reproductive cells or say gametes in both females and males . Reproductive cells are produced by meosis and somatic cells undergo mitosis for growth . The Chromosomes undergo meosis so each cell has only half the Chromosomes and fuse at fertilisation for zygote to have full set of chromosomes.

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