paper 2: Inheritance and Populations

Question 1

define gene

Answer 1

a base sequence of DNA on a chromosome which codes for the amino acid sequence of a polypeptide or functional RNA

Question 2

define allele

Answer 2

a different version of a gene

Question 3

define genotype

Answer 3

genetic constitution of an organism

Question 4

define phenotype

Answer 4

the expression of this genetic constitution and its interaction with the environment

Question 5

define a homologous chromosome

Answer 5

pair of chromosomes with same gene in same gene loci but can have different alleles

Question 6

define homozygous dominant

Answer 6

homozygous organism with 2 dominant alleles

Question 7

define homozygous recessive

Answer 7

a homozygous organism with 2 recessive alleles

Question 8

define heterozygoous

Answer 8

the allele on each homologous chromosome is different

Question 9

what does a gene being expressed mean

Answer 9

how it is transcribed into mRNA and then how mRNA is translated into a protein

Question 10

what is meant by a dominant allele

Answer 10

allele is always expressed in the phenotype

Question 11

what is meant by a recessive allele

Answer 11

allele that is only expressed in phenotype when in presence of another identical allele

Question 12

define monohybrid inheritance

Answer 12

the inheritance of a single gene on an autosome

Question 13

why are the actual results of genetic crosses rarely the same as predicted results

Answer 13

• random fertilisation of gametes
• may be small population
• some alleles may give selective advantage

Question 14

define dihybrid inheritance

Answer 14

the inheritance of 2 different genes on different chromosomes at the same time

Question 15

draw dihybrid genetic cross diagram of 2 heterozygous parents

Answer 15

Question 16

what is the rule for dihybrid crosses

Answer 16

always produce 9:3:3:1 phenotypic ratio

Question 17

define co-dominant alleles

Answer 17

both alleles are expressed in the phenotypes

Question 18

draw out the first 2 geenrations of phenotypes produces when pure breed red (C^RC^R) and white (C^WC^W) snapdragons are bread together

Answer 18

Question 19

define multiple alleles

Answer 19

more than 2 alleles in a population

Question 20

define sex-linkage

Answer 20

a gene carried on the X chromosome

Question 21

explain which sex is more likely to express the recessive alleles found on the sex chromsomes in their phenotype

Answer 21

males
- they only have one copy of X chromsome so only need one copy of recessive alele in genotype to express recessive phenotype wherease females have 2 X chromosomes so need 2 copies of recessieve allele in their genotype to express the recessive phenotype

Question 22

find phenotype ratios

Answer 22

Question 23

define autosomal linkage

Answer 23

inheritance of 2 or more genes carried on the same autosome

Question 24

find phenotypic ratios for this example

Answer 24

Question 25

define epistasis

Answer 25

the allele of one gene affects or masks the expression of another gene

Question 26

In humans, Huntington’s disease is caused by a dominant mutant allele of a gene. Draw a genetic diagram to show the possible genotypesand phenotypes of the offspring produced between a man with one allele for the disease and woman who does not suffer from the disease.

Answer 26

Question 27

In cocker spaniels, black coat colour is the result of a dominant allele and red coat colour is the result of a corresponding recessive allele.
Draw a genetic diagram to show a cross between a pure-breeding (homozygous) bitch with a black coat and a pure-breeding (homozygous) dog with a red coat.

Answer 27

Question 28

In cocker spaniels, black coat colour is the result of a dominant allele and red coat colour is the result of a corresponding recessive allele.
If the offspring of this first cross are interbred, calculate the probabilitythat any one of the offspring will have a red coat. Use a genetic diagram to show your working

Answer 28

Question 29

how do you calculate alle frequency using Hardy Weinberg

Answer 29

p + q = 1

p= dominant allels
q= recessive alleles

Question 30

how do you calculate the genotype frequency using Hardy Weinberg

Answer 30

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

p^2 = homozygous dominant
2pq = heterozygous
q^2 = homozygous recessive

Question 31

what are assumptions made by hardy weinberg

Answer 31

• mating is random
• no immigration so new new alleles indroduced
• no mutations so no new alleles created
• no selection so no alleles favoured or eliminated
• large population