Topic 3 - Genetics

Question 1

What are gametes?

Answer 1

haploid cells that contain just one copy of each chromosome ( only 23 chromosomes )

Question 2

What are gametes used for ?

Answer 2

Fertilisation - Male gamete ( sperm from the father) and female gamete ( egg from the mother) fuse together to produce a fertilised egg ( zygote )

Question 3

Why are gametes haploid ?

Answer 3

1 copy of the chromosome from each gametes join together so the fertilised cell has the right number of chromosomes ( 2 copies of each )

Question 4

Why is this useful?

Answer 4

The resulting offspring receives half its chromosomes from its mum and half from dad, so inherits features from both parents

Question 5

What cells are produced by meiosis?

Answer 5

gametes

Question 6

3 differences between mitosis and meiosis

Answer 6

• 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

Question 7

advantages of asexual reproduction

Answer 7

• 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

Question 8

disadvantages of asexual reproduction

Answer 8

• no genetic variation in population
• if environment changes and conditions become unfavourable, the whole population may be unable to cope

Question 9

advantages of sexual reproduction

Answer 9

• genetic variation in offspring and population
• chance of species surviving change in environment increases

Question 10

disadvantages of asexual reproduction

Answer 10

• 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

Question 11

DNA

Answer 11

chemical that all the genetic material in a cell is made from up

Question 12

structure of DNA

Answer 12

it is a polymer made up of repeating units called nucleotides. it is arranged as two strands coiled to form a double helix

Question 13

gene

Answer 13

small section of DNA that codes for a particular sequence of amino acids which are put together to form a protein

Question 14

genome

Answer 14

all of an organism’s DNA. Your genome controls what characteristics you develop

Question 15

structure of a nucleotide

Answer 15

it has a sugar- phosphate backbone which forms the strands
they have 4 different bases which is attached to the sugar

Question 17

complementary base pairings

Answer 17

each base in a DNA strand links to a complimentary base on the opposite strand and are held together by weak hydrogen bonds

Question 18

A pairs up with …

Answer 18

T

Question 19

G pairs up with …

Answer 19

C

Question 20

allele

Answer 20

different form of the same gene

Question 21

homozygous

Answer 21

having 2 identical alleles for a characteristic

Question 22

heterozygous

Answer 22

have 2 different alleles for a characteristic

Question 23

dominant allele

Answer 23

an allele that has an effect in both homozygous and heterozygous conditions

Question 24

recessive allele

Answer 24

an allele that only has an effect in heterozygous conditions

Question 25

genotype

Answer 25

combination of all the alleles a person has

Question 26

phenotype

Answer 26

an organisms outward appearance as a result of their genotype

Question 27

expressed

Answer 27

when the gene switches on and the protein is made

Question 28

what are most phenotypic features a result of

Answer 28

multiple genes and alleles

Question 29

male chromosomes

Answer 29

XY

Question 30

female chromosomes

Answer 30

XX

Question 31

why are recessive sex linked disorders more common in men?

Answer 31

• 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

Question 32

Codominance

Answer 32

when two alleles of a gene are expressed in the same phenotype . blood groups A and b are co dominant with each other

Question 33

genetic variation

Answer 33

-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 )

Question 34

environmental variation

Answer 34

different characteristics caused by an organism’s environment

Question 35

factors depending on both environmental and genetic variation

Answer 35

height, intelligence, health

Question 36

mutation

Answer 36

a random change in the base sequence of an organism’s DNA which means the gene is altered