In tomatoes, tall growth habit is the result of a dominant gene, D. Dwarf growth to its recessive allele, d. Smooth epidermis is due to a dominant gene P pubescent epidermis to its recessive allele p. a homozygous tall smooth vaiety was crossed with a dwarf pubescent variety, the f1 were testcrossed to dwarf pubescent. the results of the test cross were as follows.

tall, smooth-96

tall, pubescent-4

dwarf, smooth-3

dwarf pubescent-95

Are these genes linked? If so, what is the percent of crossing over?

Explanation:

Given;

Tall (D) is dominant over dwarf growth (d);

Smooth (P)  is dominant over pubescent epidermis(p).

Cross between homozygous tall, smooth( DDPP) and dwarf pubescent (ddpp);

= DDPP × with ddpp

F1 = DdPp (tall, smooth).

As given; F1  (DdPp) were crossed with dwarf pubescent (ddpp);

DdPp × ddpp

Progeny as given,

are=

tall, smooth (D_P_) -96;

tall, pubescent (T_pp) - 4;

dwarf, smooth (ddD_) - 3;

dwarf,pubescent ( ddpp)- 95.

Recombinants are= 3+4= 7

non-recombinants = 95+94= 191

Yes, these genes are linked genes.

Recombination frequency= total recombinants/ total progeny× 100

= 7/198× 100=3.535

So RF= 3.535%

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.