Unit 7: Inheritance and Evolution

Question 1

what is codominance?

Answer 1

Where both alleles are expressed in the phenotype

Question 2

Give an example of a co-dominant genotype

Answer 2

Red flower - C^R C^R

Question 3

What are multiple alleles?

Answer 3

There are more than two alleles of a particular gene

Question 4

what are autosomes?

Answer 4

22 pairs of non-sex chromosomes

Question 5

What are the sex chromosomes?

Answer 5

XX & XY

Question 6

What are sex linked genes?

Answer 6

where the gene is carried only on one type
of sex chromosome (usually X)

Question 7

how can you prove that an allele is recessive?

Answer 7

Two unaffected parents will have an affected child

• parents must therefore be heterozygous (carriers)

Question 8

How can you prove that an allele is not sex linked when it is known to be recessive?

Answer 8

Unaffected parents who have an affected daughter

• Their father would pass on the dominant allele on the X so all daughters will be unaffected

Question 9

How can you prove that an allele is dominant?

Answer 9

Two affected parents who have unaffected children

• Both parents must be heterozygous and pass on the recessive alleles

Question 10

how can you prove that an allele is not sex linked when it’s known to be dominant?

Answer 10

2 affected parents will have an unaffected daughter

• The father would pass on the dominant allele on his X so all daughters would be affected

Question 11

What is dihybrid inheritance?

Answer 11

refers to inheritance of two different characteristics

each characteristic is controlled by a different gene

Question 12

what is a phenotype

Answer 12

appearance of a characteristic

Question 13

what is a genotype

Answer 13

alleles present in an organism (e.g BB)

Question 14

why may the observed and expected ratios in a dihybrid cross not be similar?

Answer 14

small sample size
random fertilisation of gametes
epistasis
linked genes

Question 15

What are autosomal linked genes

Answer 15

genes present on the same chromosome at different loci

Question 16

Why are there fewer combination of alleles in linked genes?

Answer 16

linked genes are inherited together and theres no independent assortment

• this leads to reduced variety of genes

Question 17

Why is the number of recombinant alleles low?

Answer 17

because crossing over is rare

Question 18

What is Epistasis?

Answer 18

when two or more genes interact to contribute to a phenotype

the allele of one gene affects/masks the expression of another at another locus

Question 19

In what conditions does Epistasis occur?

Answer 19

in metabolic pathways controlled by enzymes coded for by different genes

Question 20

What happens if the enzyme in epistasis is non functional?

Answer 20

the pathway comes to a halt

Question 21

What is a species?

Answer 21

a group of organisms that can reproduce and produce fertile offspring.

Question 22

What is a population?

Answer 22

a group of organisms of the same species occupying a particular space that can reproduce to produce fertile offspring

Question 23

What is a Gene pool?

Answer 23

all the alleles of all the genes of all the individuals in a population

Question 24

What is Allelic frequency?

Answer 24

the number if times an allele of a particular gene occurs within the gene pool

Question 25

What is the Hardy-Weinberg principle?

Answer 25

mathematical model which predicts that allele frequencies in a population **will not change** from generation to generation

Question 26

What are the conditions for the Hardy-Weinberg principle?

Answer 26

- large and isolated population - mating is random - no mutations of the gene occurs - no selection

Question 27

Im a scenario where there are only 2 alleles for a gene what should the frequency of these alleles equal?

Answer 27

1.0 (100% of the population)

Question 28

What is the equation for frequency of different genotype for an allele?

Answer 28

p^2 + 2pq + q^2 = 1.0

Question 29

What does P^2 represent in the Hardy-Weinberg principle?

Answer 29

frequency of the dominant allele

Question 30

What does q^2 represent in the Hardy-Weinberg principle?

Answer 30

frequency of the recessive allele

Question 31

What is the Chi-squared test?

Answer 31

Determines a **statistical difference** between the expected and observed ratios from the result of a genetic cross

Question 32

What is a null hypothesis?

Answer 32

assumes there will be no significant difference between observed and expected frequency

Question 33

What is the equation for Chi-squared (X^2)

Answer 33

X^2 = sum ( (O-E)^2 / E )

Question 34

If the X^2 is below the critical value..

Answer 34

the null hypothesis is accepted and there is **NO** significance the probability that the difference is due to chance is more than 5%

Question 35

If X^2 is above or the same as the critical value..

Answer 35

the null hypothesis is rejected and there is a significance the probability that the difference is due to chance is less than 5%

Question 36

How do you calculate the degree of freeodm?

Answer 36

number of categories - 1

Question 37

What causes genetic variation?

Answer 37

- gene mutations - crossing over - independent segregation of chromosomes - random fertilisation

Question 38

What are the properties of characteristics influenced by genetic factors not environmental ?

Answer 38

- controlled by two genes - **expressed as phenotypes** with no intermediates - represented as distinct groups on a bar chart/pie graph

Question 39

What are the properties of characteristics that are significantly influenced by the environment?

Answer 39

- **polygenic**, controlled by many genes - no separate categories, have **range of intermediates** - produce a curve of **normal** distribution on graph

Question 40

What are selection pressures?

Answer 40

preditation disease competiton

Question 41

What is stabilising selection?

Answer 41

environment isn’t changing organisms with the mean characteristics are selected for organisms with extremes (very high/low) are less likely to survive

Question 42

What is directional selection?

Answer 42

environment is changing and selects for organisms with alleles for a phenotype towards the extreme range

Question 43

What is Disruptive selection?

Answer 43

selects phenotypes at the **two** extremes at the expense of intermediate phenotypes most important selection to bring out evolutionary change

Question 44

What is speciation

Answer 44

the evolution of new species from existing ones

Question 45

What is allopatric speciation?

Answer 45

a population splits into groups by **geographical isolation** which prevents breeding **different selection pressures** occur in the new different environments and natural selection occurs resulting in new phenotypes **allelic frequencies**become different and organisms become two different species

Question 46

What is sympatric speciation?

Answer 46

(no geographical isolation) - involves disruptive selection mutations cause organisms to not reproduce with organisms of the same species causing **reproductive isolation** results in **changes in courting behaviour** even though they live in the same habitat different gene pools occur

Question 47

What is genetic drift?

Answer 47

By chance the allele of a particular gene is passed on to the offspring more often than other alleles has greater effect in small populations where there is a smaller variety of alleles in the gene pool, so **speciation occurs more rapidly**