Biology Topic 3B

What are gemmates?

Sex cells found in the male and female reproductive system

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What are these gamets called in males and females?

Sperm and egg cell's (ovary)

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What is a haploid cell?

A cell that has half the chromosomes (23) instead of the full amount (46)

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What is fertilisation?

The exact moment the nuclei of the sperm cell and the egg cell fuse

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What is formed as a result of the sperm cell and the egg cell fertilising?

A zygote

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What does having 2 haploid cells join do to diverity?

It increases it

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Name 2 ways the egg cell is specialised?

1)Follicle cells- they surround the egg as a protective layer
2)Zona pellucida-Is a layer of protective glycoprotein that the sperm cells have to penetrate

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Name 3 ways sperm cells are specialised for there function?

1) Mitochondria neck-to provide lots of energy for swimming
2)Flagellum- helps with mobility of the sperm cell(helps it move)
3)Acrosome-has digestive enzymes that penetrate the zona pellucida

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Name the order in which the sperm travels to reach the egg cell?

Cervix>Uterus>oviduct>Ovaries>Fertilisation

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What happens in the Acrosome reaction?

The sperm cell penetrates the Zona pellucida, releasing digestive enzymes that allow it into the cell membrane.

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What is the Cortical reaction?

This happens after the Sperm has penetrated the Zona pellucida, as it triggers the egg to release cortical granules. They thicken the Zona pellucida stopping other sperm cells entering.

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What two reactions take place when the sperm reaches the egg cell?

Acrosome reaction
&
Cortical reaction.

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What is Meiosis?

The type of cell division that takes place in reproductive organs

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What 3 things happen to a reproductive cell before it undergoes the 1st and 2nd division of meiosis?

1)The DNA replicates forming 2 identical chromatids(so there are 4 chromatids in Nucleus)
2)The DNA condenses that forms a two-armed chromatid, made of sister cells.
3)The chromatids organise themselves into homologous pairs(pairs of matching chromosomes

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After the 2 divisions in meiosis how many daughter cells are formed?

4 unidentical daughter cells

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Name the 2 ways that meiosis makes genetic variation?

1)crossing over chromatids
2)Independent assortment of chromosomes

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Explain 'crossing over chromatids'?

1-when the chromatids are lined up in homologues pairs,2 chromatids from each pair twist around each other
2-they then break of the original chromatid and re-join to the other chromatid
3-recombining their genetic material
4-They contain the same genes b

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How does it increase Genetic variation?

Each cell has a different chromatid and therefore a different set alleles

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Explain independent assortment?

Homologous chromosomes line up in random orientations at the middle of the cell at metaphase as they prepare to separate, meaning that the same parent cell can produce different combinations of chromosomes in the daughter cells

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What is a locus?

The position of a gene on a chromosome

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When is a characteristic said to be sexually linked?

When the locus of the allele that codes for it is on a sex chromosome

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Why are males more likely to get sex-linked characteristics?

This is because the 'Y' chromosome is small and carries fewer genes, so no characteristic is expressed. So if the 'x' chromosome is recessive the male will have that disorder.
X^h Y

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What is a sex-linked characteristic?

characteristics that are influenced by genes carried on the sex chromosomes.

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What does it mean when 2 genes are linked?

They are on the same chromosome

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Explain how independent assortment can lead to genetic variation?

-Independent assortment means the genes can split up in any way
-so the cells produced can contain both maternal and parental chromosomes with different alleles

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Get Revising

Biology Topic 3B

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