Reproduction Flashcards
(44 cards)
what is a gamete
sex cells of an organism
For example, the sperm and egg (ovum) cells in humans
how is zygote formed
Gametes fuse during fertilisation
Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell)
how are sex cells formed
formed during meiosis and only have one copy of each chromosome, so they are haploid cells
adaptations of a sperm cell
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
Adaptations of egg cells
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
what does the sperm cell follow
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
when can fertilisation occur
If a sperm cell meets the egg cell in the oviduct
when is it most likely for fertilisation to occur
1-2 days after the female has ovulated (i.e. released an egg cell from one of her ovaries into an oviduct)
what is the acrosome reaction
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
what happens after the acrosome reaction has occurred and what is this known as
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
What do every chromosomes consist of
long DNA molecule that contains several hundred or even thousands of different genes coding for different proteins
what is a gene
base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
what is a locus
The position of a gene on a chromosome
why do genes occupy specific locus
so that the gene for a particular characteristic is always found at the same position on a particular chromosome
what can genes exist as
two or more different forms called alleles
what is an autosome
any chromosome that isn’t a sex chromosome
what is autosomally linked
if two or more genes are located on the same autosome so a non-sex chromosome
do two or more genes on the same autosome assort independently
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)
what is independent assortment
during independent assortment Genes with loci on different chromosomes are randomly distributed in gametes
what are sex linked genes
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
why are men more susceptible to sex linked genes
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
why are female less likely to show sex linked recessive condition
Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele
what happens when loci of genes are closer
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.
what is meiosis
gives rise to cells that are genetically different from each other and is the type of cell division used to produce gametes
