Linkage, sex linkage and sex determination Flashcards Preview

BLGY1232 Introduction to genetics > Linkage, sex linkage and sex determination > Flashcards

Flashcards in Linkage, sex linkage and sex determination Deck (21):
1

What is the three-point test-cross?

The standard procedure for determining the order and relative distances between genes on a chromosome.

2

What would be the result if the three genes were unlinked?

They would independently segregate to give 8 different phenotypes from within 64 genotypes in a 1:1:1:1:1:1:1:1 ratio

3

What would be the result if the three genes were linked?

8 phenotypes will result from 8 different genotypes, the ratio would depend on the number of map units between different loci.

4

What is the result of a double recombination?

The middle gene 'changing partners'

5

What are the three steps in determining the distance between relative genes on a chromosome?

1. Identify the parental combination of alleles (most frequent)
2. Identify the middle locus (the least frequent class)
3. Calculate the recombination frequency between each pair of loci

6

What does the least frequent combination indicate?

That double recombination has occurred and so gene order can be determined.

7

How can a species ensure outcrossing?

If the species has sexually dimorphic individuals.

8

What is genotypic sex determination?

Gender is determined by the genotype of the individual. Based on organisms having specific sex chromosomes that can segregate from one another in meiosis

9

What is environmental sex determinism?

Gender is determined by environmental conditions.

10

What is a dominant Y system?

Presence of a Y chromosome determines maleness. Occurs in mammals

11

Give an example of a hermaphrodite flower?

Silene Latifola

12

What happens in hermaphrodite flowers?

The presence of a Y chromosome suppresses carpel development and promotes stamen development. XXY is male.

13

What determines the gender in Drosophila?

The X to autosome ratio

14

What is heterogametic sex?

Produces two types of gametes, each carrying a different sex chromosome (male mammals).

15

What is homogametic sex?

Produces one type of gamete, all carrying the same autosome (female mammals).

16

What was sex-linkage first observed in?

Drosophila

17

Why is having two X chromosomes a problem?

You may end up with over expression of a gene

18

What is X-inactivation

Causing one random X chromosome and condensing it tightly with histones until it is inaccessible by gene expression machinery.

19

Which X chromosome is inactivated?

A random one in every cell in the body

20

In female cats why can't the co-dominant O alleles be expressed at the same time?

because one chromosome is inactivated.

21

Are female birds hetero or homogametic?

Heterogametic