Inheritance

Question 1

Define phenotype

Answer 1

The expression of an organism’s genetic constitution

Question 2

How can meiosis bring about genetic variation?

Answer 2

• Random arrangement of chromosomes during lining up
• Crossing over of chromatids before the first division

Question 3

How does random fertilisation bring about genetic variation?

Answer 3

• Gametes are haploid, contain different DNA
• The same two individuals can produce different offspring

Question 4

Monogenic inheritance

Answer 4

Where one phenotypic characteristic is controlled by a single gene

Question 5

Dihybrid inheritance

Answer 5

Two phenotypic characteristics are determined by two different genes present on two chromosomes at the same time

Question 6

What is sex linkage?

Answer 6

Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual

Question 7

Codominant alleles

Answer 7

Two dominant alleles that both contribute to the phenotype

Question 8

Autosomal linkage

Answer 8

Where two or more genes are located on the same chromosome (non sex)

Question 9

Epistasis

Answer 9

Where two non linked genes interact with one gene either masking or surpressing the other gene

Question 10

Chlorosis

Answer 10

• Plants have a change in their phenotype due to environmental factors

E.g lack of light, mineral deficiencies, virus infections which interrupt metabolism

Question 11

Animal body mass

Answer 11

• Determined by genetic and environment
• E.g obesity

Question 12

Homozygous

Answer 12

Two identical alleles for a characteristic

Question 13

Heterozygous

Answer 13

Two different alleles for a characteristic

Question 14

Continuous variation

Answer 14

A characteristic that can take any value within a range

Controlled by a number of genes

E.g leaf SA, animal mass, skin colour

Question 15

Discontinuous variation

Answer 15

A characteristic that can only appear in specific values

Controlled by one or two genes

E.g blood group, albinism, round and wrinkled pea shape

Question 16

Performing a genetic cross

Answer 16

1. State phenotype of parents
2. State genotype
3. State gametes
4. Use a punnett square
5. State proportion of genotype of offspring

Question 17

Codominance

Answer 17

Occurs when two different alleles occur for a gene which are equally dominant, so both are expressed

Question 18

Sex linkage

Answer 18

Characteristics determined by genes carried on the sex chromosomes

Question 19

Haemophilia

Answer 19

• Blood clots extermely slow due to absense of blood clotting factor
• Males cannot have a corresponding dominant allele on their Y chromosome and develop the condition

Question 20

Dihybrid cross

Answer 20

Used to show the inheritance of two different characteristics caused by two genes

Question 21

Recombination frequency

Answer 21

Measure of the amount of crossing over that has occured

RF= num of recombinant offspring/ total no of offspring

50%= no linkage, genes are on separate chromosome

Question 22

Dominant epistasis

Answer 22

If a dominant allele results in a gene having an effect on another gene

Question 23

Gene pool

Answer 23

Total of all the genes in a population at any given time

Question 24

Hardy weinberg principle

Answer 24

In a stable population with no disturbing factors the allele frequencies will remain constant from one gen to the next and there will be no evolution

• used to study evolutionary changes

Question 25

Factors affecting evolution

Answer 25

- Mutation is necessary for the existence of different alleles - Sexual selection leads to increase in allele freq that code for chars improving mating success - Gene flow is the movement of alleles between populations - Genetic drift occurs in small pops (change in allele freq due to random mutation - natural selection

Question 26

Gene pools in diff pops

Answer 26

Large pop= ensures lots of genetic diversity owing to the presence of many different genes and alleles, leading to variation Small pop= cannot adapt to change and are more likely to become extinct

Question 27

Controlling size of a pop

Answer 27

1. Density dependent factors= depedent on pop size and include compeition, predation, parasitism 2. Density independent= affect populatons of all sizes, climate change, natural disasters, seasonal change, human activities

Question 28

Bottlenecks

Answer 28

Large reductions in pop size wich last for at least one generation Gene pool is reduce and effects will be seen in future generations

Question 29

Founder effect

Answer 29

- Small pops can arise due to establishment of new colonies - An extreme example of genetic drift, small gene pools

Question 30

Stablilising selection

Answer 30

The norm or average is selected for positive selection and extremes are selected against -ve selection Results in reduction in freq of alleles

Question 31

Directional selection

Answer 31

- Change in environment and phenotype is no longer the most advantageous

Question 32

Disruptive selection

Answer 32

Extremes are selected for and the norm is selected against

Question 33

Speciation

Answer 33

- The formation of new species through the process of evolution

Question 34

During speciation

Answer 34

1. members of a pop become isolated and no longer interbreed 2. alleles undergo random mutation 3. accumulation of mutation lead to changes in phenotype

Question 35

Allopatric speciation

Answer 35

- Separation geographically - Environments are different so selection pressures are different and results in different physical adaptations - Separation of a small group may result in the founder effect, further enhancing differences

Question 36

Sympatric speciation

Answer 36

- Occurs within the same habitat - less frequent - Occurs when members of different species interbreed and form fertile offspring, hybrids - Hybrids cannot breed due to having a different number of chromosomes

Question 37

Artificial selection

Answer 37

Selection for breeding of plants or animals with desirable chars by farmers or breeders

Question 38

Inbreeding problems

Answer 38

- Limits gene pool and genetic diversity - Genetic disorders caused by recessive alleles