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Biology Mock AS 2 > Reproduction > Flashcards

Reproduction Flashcards

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1
Q

what is a gamete

A

sex cells of an organism
For example, the sperm and egg (ovum) cells in humans

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2
Q

how is zygote formed

A

Gametes fuse during fertilisation
Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell)

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3
Q

how are sex cells formed

A

formed during meiosis and only have one copy of each chromosome, so they are haploid cells

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4
Q

adaptations of a sperm cell

A

Have a flagellum (tail) that allows them to swim towards the egg cell

mitochondria which carries out aerobic respiration provides energy for flagellum to move

An acrosome that contains digestive enzymes to break down the protective glycoprotein layer (a jelly-like coating known as the zona pellucida) surrounding the egg cell - sperm cells must penetrate this layer in order to fertilise the egg

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5
Q

Adaptations of egg cells

A

Are much larger than sperm cells as most of their internal space contains food to nourish a growing embryo

Have follicle cells that form a protective coating

Have a jelly-like glycoprotein layer, known as the zona pellucida, that forms an impenetrable barrier after fertilisation by a sperm cell has occurred, to prevent other sperm nuclei from entering the egg

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6
Q

what does the sperm cell follow

A

a chemical trail released by the egg cell and travel up through the cervix to reach the uterus. Then travel into the oviduct containing the egg cell

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7
Q

when can fertilisation occur

A

If a sperm cell meets the egg cell in the oviduct

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8
Q

when is it most likely for fertilisation to occur

A

1-2 days after the female has ovulated (i.e. released an egg cell from one of her ovaries into an oviduct)

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9
Q

what is the acrosome reaction

A

the acrosome of a sperm cell releases enzymes that digest a path through the protective outer layer of the egg cell (the zona pellucida), allowing the sperm to pass through the egg cell membrane

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10
Q

what happens after the acrosome reaction has occurred and what is this known as

A

Cortical reaction

the egg cell immediately releases the contents of vesicles known as cortical granules into the space between the egg cell membrane and the zona pellucida

The chemicals contained within the cortical granules cause the zona pellucida to rapidly thicken and harden, preventing any more sperm cells from entering, ensuring only one sperm cell can fertilise the egg cell

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11
Q

What do every chromosomes consist of

A

long DNA molecule that contains several hundred or even thousands of different genes coding for different proteins

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12
Q

what is a gene

A

base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule

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13
Q

what is a locus

A

The position of a gene on a chromosome

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14
Q

why do genes occupy specific locus

A

so that the gene for a particular characteristic is always found at the same position on a particular chromosome

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15
Q

what can genes exist as

A

two or more different forms called alleles

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16
Q

what is an autosome

A

any chromosome that isn’t a sex chromosome

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17
Q

what is autosomally linked

A

if two or more genes are located on the same autosome so a non-sex chromosome

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18
Q

do two or more genes on the same autosome assort independently

A

Two or more genes on the same autosome do not assort independently during meiosis
Instead, these genes are linked and they stay together in the original parental combination
These linked genes are passed on to offspring all together (through the gametes)

19
Q

what is independent assortment

A

during independent assortment Genes with loci on different chromosomes are randomly distributed in gametes

20
Q

what are sex linked genes

A

when the inheritance of a gene is dependant on the sex of the individual as some genes are only present on one sex chromosome and not the other

21
Q

why are men more susceptible to sex linked genes

A

Most often sex-linked genes are found on the longer X chromosome
If the gene is on the X chromosome, males (XY) will only have one copy of the gene, whereas females (XX) will have two
Because males only have one X chromosome, they are much more likely to show sex-linked recessive conditions

22
Q

why are female less likely to show sex linked recessive condition

A

Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele

23
Q

what happens when loci of genes are closer

A

The closer the loci of the genes on the chromosome, the more closely linked they are. This is because they are far less likely to be separated during recombination in meiosis.

24
Q

what is meiosis

A

gives rise to cells that are genetically different from each other and is the type of cell division used to produce gametes

25
Q

how many types does the nucleus of parent cell undergo cell division

A

two rounds of division. These are:
Meiosis I
Meiosis II

26
Q

in meiosis I is nucleus diploid or haploid

A

The nucleus of the original ‘parent’ cell is diploid (2n) i.e. it contains two sets of chromosomes

27
Q

What happens before and during meiosis

A

Before meiosis I, these chromosomes replicate
During meiosis I, the homologous pairs of chromosomes are split up, to produce two haploid (n) nuclei
At this point, each chromosome still consists of two chromatids

28
Q

When does the chromosome number half

A

in the first division of meiosis (meiosis I), not the second division (meiosis II)

29
Q

what happens in meiosis II

A

the chromatids that make up each chromosome separate to produce four haploid (n) nuclei
At this point, each chromosome now consists of a single chromatid

30
Q

what are benefits of meiosis

A

Having genetically different offspring can be advantageous for natural selection

Meiosis has several mechanisms that increase the genetic diversity of gametes produced

Both crossing over and independent assortment result in different combinations of alleles in gametes

31
Q

what is crossing over

A

non-sister chromatids exchange alleles

32
Q

how does crossing over work

A

During meiosis I homologous chromosomes pair up and are in very close proximity to each other
The paired chromosomes are known as bivalents
The non-sister chromatids can cross over and get entangled
These crossing points are called chiasmata
The entanglement places stress on the DNA molecules
As a result of this, a section of chromatid from one chromosome may break and rejoin with the chromatid from the other chromosome

33
Q

what does swapping of alleles lead to

A

new combination of alleles on the two chromosomes

34
Q

what is independent assortment meiosis

A

production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during meiosis I

35
Q

what increases genetic variation in gametes

A

different combinations of chromosomes in daughter cells

36
Q

orientation of homologous pair?

A

Each pair can be arranged with either chromosome on top, this is completely random
The orientation of one homologous pair is independent/unaffected by the orientation of any other pair

37
Q

what does combination of allele depend on

A

how the pairs of homologous chromosomes were lined up

38
Q

how can you work out number of different chromosome combinations

A

formula 2n can be used, where n corresponds to the number of chromosomes in a haploid cell

39
Q

what happens by the end of meiosis

A

each orientation gives two types of gamete so there are four types al together

40
Q

how does meiosis given rise to genetic variation in gametes

A

independent / random assortment and crossing-over/chiasmata
independent assortment gives rise to new / different
combinations of (paternal and maternal) chromosomes ;
crossing over involves swapping of sections of chromatids /chromosomes

41
Q

how does crossing over differ in sex chromosomes

A

crossovers cannot form between (some sections of) the X and Y chromosome (1)
because ( they are not
homologous chromosomes / the Y chromosome is shorter / there are alleles on the X chromosome that are not on the Y chromosome ](1)

42
Q

describe the process of crossing over that occurs during meiosis

A

homologous chromosomes line up
(1)
* chiasmata form
(1)
break in {DNA / chromatid / chromosome } occurs
(1)
* genetic information exchanged between {chromatids} (1)

43
Q

events following the acrosome reaction

A

sperm cell {fuses / eg} with egg cell (membrane) ;

reference to { cortical granules / vesicles / lysosomes};

idea of (cortical granules)
{moving towards / fusing with } egg cell (surface) membrane;

reference to exocytosis (of cortical granules / vesicles / lysosomes);
.
idea of contents (of cortical granules) {secreted /released into jelly layer / eq} OR reference to cortical reaction:
idea of { hardening / thickening / eq } of { zona pellucida / jelly layer }

44
Q

compare and contrast the structure of a unfertilised egg and a zygote

A

Both made up of cell membrane and cytoplasm

both contain golgi and mitochondria in cytoplasm

unfertillised egg is haploid and zygote dipolid

unfertillised egg contain cortical granules and zygote doesnt

Biology Mock AS 2 (23 decks)

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