M6 CH20

Question 1

apply environmental and genetic factors to the phenotypic variation of body mass in humans

Answer 1

environmental:
- diet
- exercise
- food availability
genetic:
- size (taller= larger bones)
- bone density
- disease

Question 2

chlorosis is a condition in plants where the leaves go pale due to not producing enough chlorophyll.
apply genetic and environmental factors that could contribute to phenotypic variation in plants, where some leaves are pale.

Answer 2

genetic:
- alleles likely to code for green leaves
environmental:
- lack of light
- mineral deficiencies
- virus infections

Question 3

distinguish continuous and discontinuous variation.

Answer 3

continuous:
- scale
- no discrete groups
- environmental and genetic factors are contributors
e.g. leal length

discontinuous:
- discrete groups
- no scale
- usually genetically controlled
e.g. blood groups

Question 4

explain the factors during sexual reproduction that can contribute to genetic variation within a species

Answer 4

meiosis:
- crossing over
- independent assortment

• random fusion of gametes

Question 5

explain what codominance is and provide a plant example

Answer 5

2 equally dominant alleles code for 1 gene
- both alleles are expressed in the genotype
e.g. snap dragon flowers are pink (have codominance: 2 alleles (one red, one white))

Question 6

explain what is meant when a gene has multiple alleles, and what this means.
provide an example

Answer 6

• genes that have 2 or more alleles
• only 2 alleles can be present in an individual
• e.g. the immunoglobulin gene

Question 7

explain what sex linkage refers to

Answer 7

genes that are carried on the sex chromosomes

Question 8

explain why males have only one copy of certain genes, referring to sex linkage.

Answer 8

because the y chromosome is much smaller than the X, it contains almost no genetic information. therefore all the genes that are on the X chromosome can’t fit on the y chromosome

Question 9

explain how sex is determined at fertilisation

Answer 9

it depends whether the sperm that fertilised the egg contains the X or y chromosome
- if X = XX FEMALE
- if y = XY MALE

Question 10

explain what haemophilia is

Answer 10

example of a sex linked genetic disorder
- blood which clots v slowly due to absence of protein blood clotting factor

Question 11

explain why the majority of haemophilia sufferers are male, referring to sex linkage

Answer 11

if male inherits recessive allele for haemophilia on their x chromosome, they can’t have a corresponding dominant allele of their y chromosome (too small) so develop condition

Question 12

explain what is meant by a “carrier” when referring to a genetic disorder

Answer 12

someone who has the recessive allele for the disorder, but doesn’t suffer from the disorder
they will pass the allele down

Question 13

state the 5 steps in creating a genetic cross

Answer 13

1.) state the phenotype of both parents
2.) state genotypes
3.) state gametes
4.) 4x4 punnet square
5.) state proportion of each genotype

Question 14

state an example which shows codominance as well as multiple alleles

Answer 14

immunoglobulin gene
- 3 alleles present Ia Ib Io
- Ia and I*b are codominant

Question 15

explain what is meant by dihybrid inheritance

Answer 15

the inheritance of 2 different characteristics caused by 2 different genes

Question 16

state the 3 types of dihybrid inheritance, explain each

Answer 16

linked - same chromosome
unlinked - different chromosomes
epistasis - one gene controls the expression of another gene

Question 17

state the equation for calculating the recombination frequency

Answer 17

n/of recombinant frequency/ total number of offspring

Question 18

explain an example of epistasis

Answer 18

coat colour in Labradors
1 gene controls colour
1 controls melanin production
second gene controls coat colour, if no melanin is produced, then the Labrador will be yellow regardless of what the first gene codes for

Question 19

state the factors affecting evolution
(4)

Answer 19

gene flow
natural selection
genetic drift
mutations

Question 20

explain what gene flow is, and how it contributes to evolution

Answer 20

the movement of alleles between populations by emigration or immigration
changes the frequency of alleles in populations

Question 21

explain what the founder effect is

Answer 21

the development of small populations by a few isolated individuals from a larger population

Question 22

distinguish density dependant and density independent factors

Answer 22

density dependent:
- depends on population size of how the population is impacted
- e.g. predation, competition

density independent:
- affects all sizes of populations in the same way
- e.g. natural disasters, climate change

Question 23

explain what stabilising selection is
draw a graph to show how it works

Answer 23

• where the norms are selected for
• extremes selected against
• the frequency of the mean increases
• the frequency of the extremes decrease, range reduces

Question 24

explain what directional selection is
draw a graph to show how it works

Answer 24

• when an environmental change means that the norms are no longer advantageous
• the extreme phenotypes are positively selected

Question 25

explain what disruptive selection is
draw a graph to show how it works

Answer 25

• the extremes are selected for
• norms are selected against
• frequency of extremes increases and frequency of norms decreases