topic 8.1 & 8.2

Question 1

what is genetic variation

Answer 1

• new versions and combination of genes fro the survival and evolution of new species

Question 2

what re 3 ways that genetic variation occurs

Answer 2

• meiosis
• mutations
• random fertilisation

Question 3

why are human traits difficult to control

Answer 3

• humans are polygenic hence lots of genes are responsible for a trait - nature
• due to the uterus environment where it grows - nurture

Question 4

how does meiosis result in genetic variation

Answer 4

• production of haploid gametes
• when chromosomes align in pairs in metaphase 1 they can arrange with maternal and paternal on either side
• independent assortment

Question 5

how does crossing over act as a source of genetic variation

Answer 5

• during prophase 1, an enzyme cuts and sticks parts of maternal and paternal chromosomes between the homologous pairs at the chiasmata
• lots of new allele combination are created
• results in genetic variation
• potential source of mutation

Question 6

how do mutations act as a source of genetic variation

Answer 6

• there is a permanent change in the DNA
• single codon changes which affects the proteins produced
• gametes are formed (meiosis)
• somatic cell division (mitosis)

Question 7

3 examples of genetic disorders

Answer 7

• down syndrome
• cystic fibrosis
• sickle cell anaemia

Question 8

3 types of mutation

Answer 8

• point
• chromosomal
• chromosome

Question 9

point mutation

Answer 9

• change in one or a small number of nucleotides
• includes deletion, insertion & substitution

Question 10

chromosomal mutation

Answer 10

• a change to the position of genes within a chromosome

Question 11

chromosome mutation

Answer 11

• when an entire chromosome is lost or gained

Question 12

random fertilisation - egg

Answer 12

• every month a selection of ova mature
• random selection of 1 egg to be released

Question 13

random fertilisation - sperm

Answer 13

• ejaculation : 2-5cm^3 of sperm released
• 20-150 million sperm per cm^3

Question 14

genotype

Answer 14

all of the genetic information in an organism

Question 15

phenotype

Answer 15

the physical and biochemical characteristics of an organism

Question 16

homozygote

Answer 16

an individual where both the alleles coding for a particular characteristic are identical

Question 17

heterozygote

Answer 17

an individual where both the alleles coding for a particular characteristic are different

Question 18

dominance

Answer 18

when a phenotype shows dominance it is expressed whether the individual is homozygous for the characteristic or not

Question 19

recessive

Answer 19

when a phenotype is recessive it is only expressed when both alleles code for a recessive feature

Question 20

codminance

Answer 20

two versions of the same gene are expressed separately to yield different traits in an individual

Question 21

multiple alleles

Answer 21

cases where the population has more than two alleles of the same gene

Question 22

inheritance of two non-interacting genes

Answer 22

• they will be inherited independently of each other
• the expected ratios of offspring with each characteristic will be the same as if the genes were considered seperately

Question 23

what is the ratio is dihybrid inheritance

Answer 23

9 : 3 : 3 : 1

Question 24

9 : 3 : 3 : 1 ratio explained

Answer 24

1. the four different gametes arise because the chromosomes arrange randomly during meiosis
   
   • AB ab Ab aB -> gametes
2. the ratio is all combinations of two 3 : 1 ratios
   - (3P + 1p) (3T + 1t) = (PT + 3Pt + 3pT + pt
3. probability of purple and tall is given by the probability of purple times probability of tall
   
   • 3/4 x 3/4 = 9/16

Question 25

what are autosomes

Answer 25

any chromosome that is not involved in inheritance of sex

Question 26

autosomal linkage

Answer 26

• genes located on the same chromosome may be inherited together - autosomal linkage

Question 27

result of autosomal linkage

Answer 27

• most gametes have the combination of alleles found in parents’ chromosomes
• only when DNA is swapped between chromosomes in crossing over can recombinant gametes be produced

Question 28

how can meiosis bring about autosomal linkage

Answer 28

• crossing over
• new combinations of alleles can be produced in gametes as a result of crossing over

Question 29

linked genes

Answer 29

• do not show independent assortment as the combinations of alleles passed down from parents will tend to stay together

Question 30

demonstrating linkage - Drosphila

Answer 30

• flies normally have grey bodies & long wings
• recessive alleles exist for black bodies & vestigial wings
• G, L, g, l

Question 31

offspring produced by crossing

Answer 31

GL = 965
Gl = 206
gL = 185
gl= 944

not a 1: 1: 1: 1 ratio that was expected from this cross

Question 32

genotype
possible gametes
offspring
phenotype
probability

Answer 32

• GL, gl, gl gl
• GL gl gl
• GL gl gl gl
• grey long, black vestigial
• 1/2, 1/2

Question 33

what does linkage do to the number of parental type offspring

Answer 33

• the number of parental type offspring is higher than recombinants

Question 34

sex linkage

Answer 34

• occurs when genes have their locus on the X chromosome

Question 35

e.g. of sex linkage

Answer 35

haemophilia

Question 36

what is haemophilia

Answer 36

• a disorder caused by the recessive allele of a gene on the X chromosome
• it is more common in males because the Y chromosome does not carry a copy of the gene
• the allele on the one X chromosome will be expressed

Question 37

features of sex linkage in humans

Answer 37

• males always have XY and females XX
• males are more likely to be affected because they can’t be heterozygous
• heterozygous females are carriers