3B Reproduction and Inheritance

Question 1

Sperm cell specialisation

Answer 1

Haploid nucleus: 23 Chromosomes to ensure a zygote has the correct number of chromosomes
flagellum: improve motility to swim towards egg
acrosome: contains digestive enzymes to break down zona pellucida
Midpiece: contains lots of mitochondria to produce energy for swimming

Question 2

Egg cell specialisation:

Answer 2

Haploid nucleus: 23 chromosomes to ensure a zygote has the correct number
Follicle cells: protective coating on the outside
Zona pellucida: glycoprotein layer for protection

Question 3

fertilisation

Answer 3

Sperm swim into the oviduct
The acrosome fuses with the zona pellucida releasing digestive enzymes that allow the sperm to move through it
The sperm head fuses with the cell membrane of the egg cell, triggering the cortical reaction. Cortical granules release their contents which cause the zona pellucida to thicken, making it impenetrable and ensuring only one sperm cell fertilises the egg.
The nucleus of the sperm cell enters the egg cell and fuses with the egg cell nucleus (zygote formed)

Question 4

mitosis vs meiosis

Answer 4

mitosis two vs meiosis four daughter cells
mitosis diploid cells vs meiosis haploid gametes
mitosis genetically identical vs meiosis different

Question 5

How does meiosis increase genetic variation

Answer 5

Crossing over- the chromatids of homologous pairs twist around each other at chiasma until they break off and recombine their genetic material, giving them a different combination of alleles
Independent assortment- Different combination of maternal and paternal chromosomes

Question 6

What does it mean when genes are linked

Answer 6

Genes with loci on the same chromosome
Genes with closer loci are more closely linked as the chances of chiasma forming between them are much lower.

Question 7

Sex linked characteristics and disorders

Answer 7

The locus of an allele is on the sex chromosome.
The y chromosome carries fewer genes meaning males have only one allele for sex linked characteristics, and the characteristic will be displayed even if its recessive.
This includes color blindness and haemophilia as the alleles for these are on the x chromosomes