Topic 3 - Genetics Flashcards
What are gametes?
haploid cells that contain just one copy of each chromosome ( only 23 chromosomes )
What are gametes used for ?
Fertilisation - Male gamete ( sperm from the father) and female gamete ( egg from the mother) fuse together to produce a fertilised egg ( zygote )
Why are gametes haploid ?
1 copy of the chromosome from each gametes join together so the fertilised cell has the right number of chromosomes ( 2 copies of each )
Why is this useful?
The resulting offspring receives half its chromosomes from its mum and half from dad, so inherits features from both parents
What cells are produced by meiosis?
gametes
3 differences between mitosis and meiosis
- meiosis produces 4 cells compared to 2
- meiosis doesn’t produce identical cells but mitosis does
- meiosis produces cells with half the number of normal chromosomes
advantages of asexual reproduction
- organisms can reproduce whenever conditions are favourable
- lack of need to find a mate, less effort
- much faster reproductive cycle which means they can produce lots of offspring very quickly
disadvantages of asexual reproduction
- no genetic variation in population
- if environment changes and conditions become unfavourable, the whole population may be unable to cope
advantages of sexual reproduction
- genetic variation in offspring and population
- chance of species surviving change in environment increases
disadvantages of asexual reproduction
- organisms need to find and attract mates to reproduce with, which takes time and energy
- finding a mate can be hard if individuals are isolated
DNA
chemical that all the genetic material in a cell is made from up
structure of DNA
it is a polymer made up of repeating units called nucleotides. it is arranged as two strands coiled to form a double helix
gene
small section of DNA that codes for a particular sequence of amino acids which are put together to form a protein
genome
all of an organism’s DNA. Your genome controls what characteristics you develop
structure of a nucleotide
it has a sugar- phosphate backbone which forms the strands
they have 4 different bases which is attached to the sugar
complementary base pairings
each base in a DNA strand links to a complimentary base on the opposite strand and are held together by weak hydrogen bonds
A pairs up with …
T
G pairs up with …
C
allele
different form of the same gene
homozygous
having 2 identical alleles for a characteristic
heterozygous
have 2 different alleles for a characteristic
dominant allele
an allele that has an effect in both homozygous and heterozygous conditions
recessive allele
an allele that only has an effect in heterozygous conditions
genotype
combination of all the alleles a person has
phenotype
an organisms outward appearance as a result of their genotype
expressed
when the gene switches on and the protein is made
what are most phenotypic features a result of
multiple genes and alleles
male chromosomes
XY
female chromosomes
XX
why are recessive sex linked disorders more common in men?
- sex linked disorders are usually due to a faulty allele on the X chromosome because X chromosomes are bigger
- As men only have one X chromosome they only need 1 copy of the recessive faulty allele
- but as women have 2 X chromosomes they need 2 copies of the allele
Codominance
when two alleles of a gene are expressed in the same phenotype . blood groups A and b are co dominant with each other
genetic variation
-caused by organisms having different alleles which lead to differences in phenotype
- sexual reproduction which means no two members of a species are the same ( apart from identical twins )
environmental variation
different characteristics caused by an organism’s environment
factors depending on both environmental and genetic variation
height, intelligence, health
mutation
a random change in the base sequence of an organism’s DNA which means the gene is altered
