L4: Sex Determinatino

Question 1

What is monoecious?

Answer 1

Both male & female reproductive structures in the same organisms

Question 2

What is dioecious?

Answer 2

Individuals possessing only male/female reproductive structures

Question 3

What determines sex in dioecious organisms?

Answer 3

Genetic or environmental factors

Question 4

Define intersex

Answer 4

Individuals of an intermediate sexual condition (infertile)

Question 5

What is the female reproductive structures in a plant made up of?

Answer 5

Stigma + pistil

Question 6

What is the male reproductive structure in the plant?

Answer 6

Stamen

Question 7

Production of female gametes in the pistil

Answer 7

• Diploid megaspore mother cell undergoes meiosis to produce megaspores (4 haploid nuclei’s)
• 3 of the 4 nuclei degrade, left with a megagametophyte (1 haploid nucleus)
• it undergoes 3 rounds of mitosis to produce an embryo sac of 8 haploid nuclei

Question 8

Where are male gametes (pollen) formed from?

Answer 8

Diploid microspore mother cells via meiosis

Question 9

Where are female gametes formed from?

Answer 9

Megaspores
- Only 1 of 4 haploid survives

Question 10

What are the different nucleii’s in the embryo sac in the pistil?

Answer 10

3- antipodal nucleii
2- endosperm nucleii
2- synergids
1- oocyte nucleus

Question 11

Which nucleus contributes DNA to the next plant?

Answer 11

Oocyte nucleus

Question 12

Describe the events of pollination & double fertilisation

Answer 12

1) Pollen transfer from stamen (male) to stigma (women)
2) Pollen tube grows towards embryo sac
3) 2 sperm nuclei enter embryo sac

Question 13

What do the sperm nucleus unites with in the embryo sac?

Answer 13

1 sperm nucleus unites with 2 endosperm nucleii

1 sperm nucleus unites with haploid oocyte nucleus

Question 14

Scientific term for 1 sperm nucleus unites with 2 endosperm nucleii

Answer 14

Triploid endosperm nucleus

Question 15

Scientific term for 1 sperm nucleus unites with haploid oocyte nucleus

Answer 15

Diploid zygote nucleus

Question 16

Define homogametic

Answer 16

Only produce 1 type of gametes, carrying a single X chromosome (XX)

Question 17

Define heterogametic

Answer 17

Produce 2 types of gametes, X & Y chromosome

Question 18

What is aneuploidies?

Answer 18

Caused by non-disjunction
Failure of homologous chromosomes to separate properly during meiosis

Question 19

Is the 47, XXY (Klinefelter Syndrome) male or female?

Is the 45, X (Turner Syndrome) male or female?

Answer 19

1) Male, but sterile
2) Female, but infertile

Question 20

What does the SRY gene (sex-determing region of Y) encode for?

Answer 20

Testis Determing Factor (TDF)

Question 21

Features of the SRY

Answer 21

Only part of Y chromsome required for male development
- Initiates testis development at week 6 of embryogenesis

NO SRY- female development

Question 22

What region determines male development?

Answer 22

SRY

Question 24

When does the differentiation of male & female start happening in embyrogenesis?

Answer 24

6th week

Question 25

What gene does SRY activate for testis development?

Answer 25

Sox9

Question 26

What 2 hormones does the developing testes produce, and what are their functions?

Answer 26

1) Testosterone -> promotes development of Wolffian duct into male reproductive structures 2) anti-Mullerian Hormone (AMH) -> causes Mullerian ducts to degenerate

Question 27

What reproductive structures does the Wolffian duct develop into?

Answer 27

1) Epididymis: sperm maturation 2) Vas deferens (transport) 3) Seminal vesicle (storage of seminal fluid)

Question 28

What happens to gonads if SRY is absent?

Answer 28

Gonadal structures develop into ovaries - Wolffian duct degenerates - Mullerian duct gives rise to oviduct, uterus, and upper part of vagina

Question 29

# D Difference between primary vs secondary sexual differentiation

Answer 29

Primary: Determined by SRY e.g presence; testes absence: ovaries Secondary: Controlled by sex hormones e.g testosterone oestrogen

Question 30

Does the sperm/egg determine sex of offspring in birds?

Answer 30

Egg

Question 31

Chromosomes in birds

Answer 31

Females: ZW Males: ZZ

Question 32

How is dosage compensation achieved?

Answer 32

Females have 2 X chromosomes, could lead to double gene expression SO 1 X chromosome is randomly inactivated early in development

Question 33

How is the X chromosome inactivated?

Answer 33

Xic contains the Xist gene on chromosome, leading to it producing a long RNA that silences 1 X chromosome

Question 34

What is a Barr body?

Answer 34

Inactivate X chromsome found in female mammals

Question 35

What is Lyonization and who is it named after?

Answer 35

A process of X chromosome inactivation in female mammals, named after Mary Lyon

Question 36

What is the difference between the ZZ/ZW system and the XX/XY system of sex determination?

Answer 36

The XX/XY system has homogametic females, while the ZZ/ZW system has homogametic males