patterns of inheritance

Question 1

what is a locus

Answer 1

specific position of a gene on a chromosome

Question 2

what is co-dominance

Answer 2

pairs of alleles which are both expressed when present red flower + white flower = pink flower

Question 3

what 2 processes cause genetic mutation?

Answer 3

• random mutation
• meiosis/sexual reproduction

Question 4

what are physical agents of creating mutagens

Answer 4

ionising radiation e.g. X-rays

Question 5

what is polyploidy

Answer 5

cell has extra set of chromosome

Question 6

what is non-disjunction in cell division?

Answer 6

separation fails to occur causing both sister chromatids to be pulled to one side of the cell

Question 7

environmental variation examples

Answer 7

hair length, accent

Question 8

environmental and genetic variation examples

Answer 8

skin colour, height, weight

Question 9

what is chlorosis and why is it an example of variation?

Answer 9

less chlorophyll = causing yellow leaves - it is an example of variation as the plant all have correct genes, chlorosis is affected by lack of light, and mineral deficiencies.

Question 10

which form of data has a higher range of intermediates?

Answer 10

continuous

Question 11

what do F2 ratios tell us?

Answer 11

if recessive allele is found in F2, both F1 parents must be heterozygous.

Question 12

what are the steps of working out a Punnett square / dihybrid cross?

Answer 12

1. find parent genotype
2. use foil to work out gamete genotype
3. set out 4 x 4 Punnett square
4. combine possible gametes
5. determine phenotype ratio

Question 13

why are males described as hemizygous?

Answer 13

because they are haploid for X-linked gene.

Question 14

features of haemophilia

Answer 14

• unable to clot blot fast
• gene found on non-homologous region of X-chromosome.

Question 15

why can males never be a carrier?

Answer 15

if they inherit the faulty gene on chromosome X then they are bound to have the disease.

Question 16

what is the relevance of “inactivation of X chromosomes in females?’

Answer 16

to avoid females expressing double number of genes from X chromosome, one is inactivated in every nucleus.
Happens randomly during embryonic development.

Question 17

what is an autosome?

Answer 17

non sex chromosome

Question 18

what is autosomal linkage?

Answer 18

two genes on the same non sex chromosome

Question 19

which type of autosome can undergo independent assortment?

Answer 19

non linked because each one can move to one side where as linked can’t split

Question 20

what is meant by autosomal ‘linkage’

Answer 20

genes are on the same chromosome so likely to be inherited together and do not undergo independent assortment.

Question 21

what is recombinant gamete

Answer 21

combination of alleles

Question 22

hypostatic gene

Answer 22

the second gene loci that is masked by the epistatic gene

Question 22

what is epistasis?

Answer 22

the interaction of non-linked gene (independent assortment) loci where one masks the expression of the other gene.

Question 23

what is meant by complimentary gene action?

Answer 23

genes work together to code for two enzymes that work in succession e.g. catalysing sub sequential steps of the metabolic pathway.

Question 24

describe what is meant by recessive antagonistic epistasis

Answer 24

homozygous presence of a recessive allele at the first locus that prevents the expression of another allele at a second locus.

Question 25

describe what is meant by dominant antagonistic epistasis

Answer 25

if the epistatic allele is dominant, then having at least one copy of it will mask the expression of other gene = working antagonistically.

Question 26

what are the three types of selection

Answer 26

- stabilising - directional - disruptive selection

Question 26

what ratio does recessive epistasis suggest?

Answer 26

9:3:4

Question 27

what ratio does dominant epistasis suggest?

Answer 27

12:3:1

Question 28

list the key words of natural selection

Answer 28

random mutation migration variation selection pressures selective advantage beneficial allele allele frequencies

Question 29

when does directional selection occur?

Answer 29

when there is a change in environment, and species with alleles form an extreme phenotype are more likely to survive + reproduction. Over many generations there is a gradual shift in the optimum value for trait.

Question 30

what is genetic drift

Answer 30

change in allele frequency in a population due to chance

Question 30

when does disruptive selection occur?

Answer 30

a type of natural selection where the extreme values are selected over the intermediate.

Question 31

what is a genetic bottle neck

Answer 31

when former population shrinks then new population rises again with advantageous alleles.

Question 31

how can gene pool be narrowed?

Answer 31

- bottle neck - founder effect

Question 32

similarities between founder effect and genetic bottle neck

Answer 32

- involve inbreeding - result in new population that carries alleles that are different from original group.

Question 32

what is the founder effect?

Answer 32

new population is established from a very small number of individuals who originate from a larger population. This new population is likely to be less genetically varied.

Question 33

difference between founder effect and genetic bottle neck

Answer 33

bottle neck populations are killed, whereas founder effect occurs when populations are geographically separated.

Question 34

give three impacts of a small populations

Answer 34

- loss of genetic diversity - inbreeding - rise in genetic disorders

Question 35

what factors affect the genetic diversity within a gene pool

Answer 35

- population size - mutation rate - migration - natural selection - genetic drift - isolation of species (founder)

Question 36

what is allopatric speciation? (geographical)

Answer 36

formation of two different species from one original species due to geographical isolation.

Question 37

what is sympatric speciation? (reproductive)

Answer 37

formation of two different species from one original species, due to reproductive isolation, while the populations inhabit the same location.

Question 38

what is artificial selection?

Answer 38

selective breeding of organism involving humans choosing desired characteristics

Question 39

how can genetic diversity be increased in a population (by what process?)

Answer 39

hybrid vigour -> crossing over 2 varieties who are likely to reproduce heterozygous individuals, lowering the chance of recessive disorders.

Question 40

what are the ethical issues of artificial selection?

Answer 40

- unfamiliar environment for species can lead to both psychological and physical distress - violation of animal rights

Question 41

what are the counter points to the unethical nature of artificial selection?

Answer 41

- increases crop yield = boosts economy - greater breeding in plants and animals to allow their groups to survive which helps endangered species - quicker and efficient, get desirable characteristics e.g. size, milk yield.