sex determination

Question 1

sex determining mechanisms

Answer 1

1. environmental
2. genes
3. haplo-diploidy
4. sex chromosomes to autosome ratio
5. sex chromosomes

Question 2

1. environmental

Answer 2

incubation temp
- synthesis of sex hormones is temp sensitive

Question 3

2. genes

Answer 3

• a particular genotype may change the expected sexual phenotype
  eg: mutant allele at a locus on the x chromosome

Question 4

3. haplodiploidy

Answer 4

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Question 5

4. sex chromosomes to autosome ratio

Answer 5

• sex is determined by the ratio of X chromosomes

Question 6

5. sex chromosomes

Answer 6

• y chromosome is responsible for producing testes
• femaleness is a result of not inheriting a y chromosome

Question 7

sex linkage def

Answer 7

a gene found on one of the types of sex chromosome but not the other
eg: colourblinness (gene is controled on X chromosome)

Question 8

the reciprocal cross

Answer 8

• is used to determine if a gene locus is on a sex chromosome
• if a locus is on a sex chromosome, the phenotypic ratio in the offspring of the reciprocal crosses will be different

Question 9

unbalanced gene dosage

Answer 9

for an x linked trait, females have 2x gene products of males
- this is balanced through dosage compensation
- x inactivation
- double expression of x linked genes in males

Question 10

dosage compensation mehcanisms (x inactivation)

Answer 10

in early embryonic development of a female, one x is switched off random
- random in humans
- equalise gene production b/w males and females