6.1.2 patterns of inheritance

Question 1

monohybrid inheritance

Answer 1

genetic cross with alleles at 1 locus
e.g. Tt x Tt

Question 2

dihybrid inheritance

Answer 2

2 genes inherited on unlinked chromosomes so 2 characteristics at the same time
e.g. RrTt

Question 3

why is each gamete equally as likely in dihybrid inheritance

Answer 3

independent assortment

Question 4

ratio for heterozygous dihybrid cross

Answer 4

9:3:3:1

Question 5

codominance

Answer 5

1 gene with multiple alleles that are both expressed

Question 6

sex linkage

Answer 6

genes located on sex chromosomes
sex determining genes carried on non-homologous region

Question 7

why are males more likely to present sex linked genes

Answer 7

XY only needs 1 copy of recessive allele to show characteristic, XX needs both

Question 8

chi squared test

Answer 8

= sum of ((observed-expected)^2/expected)

degrees of freedom = no. of categories -1

less than critical value - no sig diff = accept null hypothesis

Question 9

autosomal linkage

Answer 9

more than 1 gene on same non-sex chromosome so inherited together
causes recombinant phenotypes

Question 10

what exactly causes recombinant phenotypes

Answer 10

crossing over in prophase 1 when bivalents form

Question 11

epistasis

Answer 11

multiple alleles controlling phenotype, expression of one gene affects another

Question 12

dominant epistasis

Answer 12

dominant allele masks other gene - only one copy of dom allele needed

Question 13

what is the heterozygous cross ratio for dominant epistasis

Answer 13

12:3:1

Question 14

recessive epistasis

Answer 14

recessive allele masks other gene - 2 copies of rec needed

Question 15

what is the heterozygous cross ratio needed for recessive epistasis

Answer 15

9:3:4

Question 16

hardy weinberg

Answer 16

model to calculate allele frequency of a gene in a population

Question 17

hardy weinberg allele frequency

Answer 17

p+q=1

Question 18

hardy weinberg genotype frequency

Answer 18

p^2 + 2pq + q^2 =1

Question 19

p in hardy weinberg means

Answer 19

dominant

Question 20

q in hardy weinberg means

Answer 20

recessive

Question 21

what does hardy weinberg assume

Answer 21

no immigration/emmigration
isolated
no natural selection
no mutation
large population
random mating

Question 22

heritable

Answer 22

can be passed down from parents
some may be caused by environment

Question 23

discontinuous variation

Answer 23

qualitative
definite categories
monogenic

Question 24

continuous variation

Answer 24

quantitative
wide range of variation
polygenic

Question 25

phenotypic variation

Answer 25

phenotype determined partly genotype, partly environment

Question 26

stabilising selection

Answer 26

selects for the norm - being average is advantageous

Question 27

disruptive selection

Answer 27

speciation occurs as species becomes incompatible due to interbreeding

Question 28

directional selection

Answer 28

environmental factor changes so so individuals have a selective advantage

Question 29

genetic drift

Answer 29

change in allele frequency due to chance

Question 30

founder effect

Answer 30

unusual genes in smaller populations that have moved away from a large population so speciation

Question 31

bottleneck

Answer 31

catastrophic event - reduces population to a small number, recovers and only genes in survivors are passed down so variation doesn't increases

Question 32

allopatric speciation

Answer 32

geographical isolation of 2 populations -variation always present -diff conditions, diff selection pressure, diff alleles -diff allele frequencies -seperate gene pools so no interbreeding- 2 species

Question 33

sympatric speciation

Answer 33

same environment -mutations cause diff phenotypes so individuals are reproductively isolated -no gene flow -gene pools seperated -diff alleles selected and passed on, can't interbreed - 2 species

Question 34

prezygotic barriers in reproductive isolation

Answer 34

courtship behaviour not recognised so no mating mechanical barrier as different sized gentilia leads to incompatibility physiological barrier as cross pollination between species happens but no fertilisation as pollen tube doesn't grow

Question 35

postzygotic barriers in reproductive isolation

Answer 35

hybrid not viable hybrid is viable but sterile