32) Unit 2 - Sex Determination

Question 1

what are hermaphrodites

Answer 1

organisms with both male and female reproductive organs

Question 2

Name the environmental conditions that can affect the sex ratio of offspring and give an example for each

Answer 2

• Temperature: crocodile eggs are male in temps <31 and female in temps >32
• Size: sex can change within individuals of some species because of size. clown fish live in groups with many small females and 1 large female. When the large female is removed the largest male becomes a female
• Competition: In lemur mouse if a female detects the urine of another female she produces a male
• Parasitic Infection: In insects infected by a certain parasite the parasite kills the male eggs or turns them into females

Question 3

name the factors that can determine sex

Answer 3

• Genetic

* Environmental

Question 4

what determines sex in live bearing mammals

Answer 4

X and Y chromosome

Question 5

what is homogametic and hetrogametic

Answer 5

Homo:
(XX) same type of chromosome

Hetro:
(XY) different types of chromosomes

Question 6

describe what region creates the male characteristics and genetalia and what does this region do?

Answer 6

SRY, is the sex determining region of y chromosome which acts as a master switch which switch on other genes

Question 7

why do males have sex linked patterns of inheritance where they have a greater chance of being affected by certain recessive conditons

Answer 7

Because there Y chromosomes lack many genes found on the X chromosome

Females 2 copies of the recessive allele to be affected whereas males only need one.

Question 8

why are females usually carriers of recessive diseases yet show no deleterious effect

Answer 8

Because they need 2 copies to show the disease

Question 9

Give two examples of sex linked recessive conditions that males can suffer from

Answer 9

• Colour blindness

* Haemophillia

Question 10

why do females not have a double dosage of genes

Answer 10

because they undergo x-inactivation where random genes on either X alleles are inactivated

Question 11

why is the consequences of double dosage of genes

Answer 11

Could be harmful to cells

Question 12

why are carriers less likely to be affected by harmful mutations on the X chromosomes

Answer 12

Because the gene with the mutation is likely to be inactivated during X-inactivation