Biol4 - Inheritance + Genetics Definitions Questions

Question 0

Dominant allele?

Answer 0

An allele which is always expressed

Question 1

Gene pool?

Answer 1

All of the alleles of all the genes of all the individuals in a population at a given time

Question 2

Recessive allele?

Answer 2

An allele which is only expressed when in it’s homozygous state

Question 3

Homozygous?

Answer 3

When a diploid organism carries two identical alleles

Question 4

Heterozygous?

Answer 4

When a diploid organism carries two different alleles

Question 5

Self cross

Answer 5

When the offspring are bred with themselves

Question 6

Codominance?

Answer 6

When both alleles are equally dominant and therefore both expressed in the phenotype

E.g. Snapdragon plant, red and white makes pink

Animals cows and cat patchy or tortoiseshell

Question 7

Multiple alleles?

Answer 7

When a gene has 3 or more alleles

e.g. Blood groups I(A) I(B) both dominant can create A, B or AB blood types and

I(O) which is recessive and only when both is blood type O

Question 8

Sex linked?

Answer 8

When a characteristic is determined by a gene on the X chromosome, e.g. Haemophilia, colour blindness and muscular dystrophy

Question 9

How natural selection produces changes within a species (4)

Answer 9

~in a population characteristics differ between members as they have different alleles (also mutation of alleles could’ve occured)
~survival and reproduction of individuals within a population is varied due to disease, predation and intraspecific competition
~organisms whose characteristics best fit the environment are more likely to survive and breed and pass on alleles to the next generation
~therefore frequencies of advantageous alleles increases

Question 10

What are the Harvey-Weinberg equations? (2)

Answer 10

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

~p + q = 1

Question 11

If B is the dominant allele for brown eyes and b is the recessive allele for blue eyes, what percentage of the population is heterozygous if 51% have Brown eyes?

Answer 11

~q^2 = 0.49/49% (as 51% have brown eyes so only 49% ie q^2 have blue) or q = 0.7 (square root of 49)
~1-0.7=0.3, ¥ p = 0.3
~2pq is heterozygous so 2 x 0.7 x 0.3 = 0.42
¥ 42% are heterozygous

(To check use full equation so 0.3^2 + (2x0.3x0.7) + 0.7^2 = 1 :) )

Question 12

A breeder crossed a male brown dog with a female brown dog on a number of occasions producing 8 brown pups and 4 cream pups, explain the evidence that allele for cream fur is recessive (1)

Answer 12

~parents are heterozygous
Or
~pups receive cream allele from brown parents

Question 13

If you have a brown dog with genotype Bb and cream dog with genotype bb, what would be the ratio of brown to cream pups produced? (1)

Answer 13

1:1

Genetic cross produces: Bb, bb, Bb, bb

2 brown pups, 2 cream pups, hence one to one

Question 14

Why can the offspring produced have different phenotypes/genotypes from those predicted from genetic diagrams/crosses? (3)

Answer 14

~fusion/fertilisation of gametes is random
~offspring ratios are probabilities
~small sample

Question 15

If you had B coding for black, b coding for chocolate and bi coding for cinnamon, stated in order of dominance, is it possible to produce offspring with only chocolate fur? (3)

Answer 15

~possible if parents are homozygous bb
~however don’t know genotype of chocolate cat, could be bbi
~hence two chocolate cats could produce cinnamon kittens

Question 16

What does Hardy-Weinberg predict about frequency of the recessive allele after 10 generations? (1)

Answer 16

Stays the same

Question 17

The frequency of a recessive allele in a population has decreased, what type of natural selection has occured in this population? explain how this type of selection has caused a decrease in the frequency of the recessive allele (2)

Answer 17

~directional
~dominant allele is advantageous, more likely to survive to reproduce

(If allele frequencies remain same its stabalising selection)

Question 18

There are 960 purple monsters (dominant) and 40 green monsters, what percentage of the monsters are heterozygotes? (3)

Answer 18

~find % of population is homozygous recessive, total alleles 960 + 40 = 1000, total homozygous recessive allele = 40, 40/1000 x100 = 4 % = 0.04 = q^2
~calculate q by square rooting q^2, square root 0.04 = 0.2, p = 1 - 0.2 = 0.8
~hence % of heterozygotes = 2 x 0.8 x 0.2 = 32% heterozygous

Question 19

Why flies which lay up to 400 eggs and develop into adults in 7 to 14 days are good for studying for genetic crosses (2)

Answer 19

~large number of eggs, large sample size

~eggs develop into adult in short time so results obtained quickly

Question 20

males more likely than females to show a phenotype produced by a recessive allele carried on the X chromosome? Explain why (2)

Answer 20

~males can only have one allele (for this gene)

~females must be homozygous recessive to show a phenotype produced by a recessive allele