Inheritance

Question 1

What is a genome?

Answer 1

All the DNA in a cell or organism.

Question 2

What else can ‘genome’ mean?

Answer 2

All the genes, alleles, genetic material, or code in a cell, organism, or person.

Question 3

Another way to define a genome?

Answer 3

The total number of DNA bases in a cell or organism.

Question 4

Name one cause of genetic variation.

Answer 4

Mutation.

Question 5

Name another cause of genetic variation.

Answer 5

Crossing over.

Question 6

Name a third cause of genetic variation.

Answer 6

Independent segregation or assortment of homologous chromosomes.

Question 7

Name a fourth cause of genetic variation.

Answer 7

Random fusion of gametes, fertilisation, or mating.

Question 8

What does genetic variation produce?

Answer 8

New combinations of alleles.

Question 9

How can a single base substitution change a polypeptide?

Answer 9

It changes the sequence of amino acids (primary structure).

Question 10

How does this affect the protein structure?

Answer 10

Changes hydrogen, ionic, or disulfide bonds.

Question 11

What does this bond change alter?

Answer 11

The tertiary structure of the protein.

Question 12

What is meant by genotype?

Answer 12

The genetic constitution of an organism.

Question 13

What is phenotype?

Answer 13

The expression, appearance, or characteristic due to genotype or alleles.

Question 14

What else influences phenotype?

Answer 14

Interaction with the environment.

Question 15

What is a dominant allele?

Answer 15

An allele expressed in both homozygotes and heterozygotes.

Question 16

What is a recessive allele?

Answer 16

An allele only expressed in homozygotes; not expressed if a dominant allele is present.

Question 17

What must affected offspring have if the trait is dominant?

Answer 17

At least one affected parent.

Question 18

What about unaffected parents in dominant traits?

Answer 18

Unaffected parents only have unaffected offspring.

Question 19

If two affected parents have an unaffected child, what does this mean?

Answer 19

Both parents must be heterozygous.

Question 20

Can unaffected parents have affected offspring if the trait is recessive?

Answer 20

Yes, if both parents are heterozygous carriers.

Question 21

What is codominance?

Answer 21

Both alleles are expressed in the phenotype.

Question 22

How do multiple alleles of a gene arise?

Answer 22

Through mutations at different positions in the gene.

Question 23

What is epistasis?

Answer 23

When the allele of one gene affects or masks the expression of another gene in the phenotype.

Question 24

What is gene linkage?

Answer 24

Genes or loci located on the same chromosome.

Question 25

Expected ratio for monohybrid cross with heterozygous parents?

Answer 25

3:1 (dominant : recessive).

Question 26

Expected ratio for dihybrid cross with heterozygous parents?

Answer 26

9:3:3:1.

Question 27

Expected ratio with epistasis?

Answer 27

9:4:3 or 15:1 or 9:7 (varies by type).

Question 28

Expected ratio for autosomal linkage with no crossing over?

Answer 28

3:1 (dominant : recessive), no recombination.

Question 29

What is sex linkage?

Answer 29

Expression of an allele depends on the individual’s gender because the gene is on a sex chromosome.

Question 30

Why are males more likely to show recessive sex-linked traits?

Answer 30

Males have only one copy of the allele, so recessive alleles are always expressed.

Question 31

Why might females not show the trait?

Answer 31

Females need two recessive alleles to express the trait; they can be heterozygous carriers.

Question 32

Suggest one reason phenotypic ratios differ from expected.

Answer 32

Small sample size.

Question 33

Suggest another reason.

Answer 33

Random fusion or fertilisation of gametes.

Question 34

Name a genetic factor that causes deviation.

Answer 34

Linked genes or sex linkage.

Question 35

Another genetic factor?

Answer 35

Epistasis.

Question 36

Another possible cause?

Answer 36

Lethal genotypes.

Question 37

What is a gene pool?

Answer 37

All the alleles present in a population.

Question 38

What does the Hardy-Weinberg equation predict?

Answer 38

The frequency or proportion of alleles of a gene.

Question 39

What condition must be met for allele frequencies to stay constant?

Answer 39

No mutation, no selection, large population, genetic isolation, random mating, no migration.

Question 40

What is the Hardy-Weinberg equation?

Answer 40

p² + 2pq + q² = 1

Question 41

What do p and q represent?

Answer 41

p = frequency of one allele (usually dominant), q = frequency of the other allele (usually recessive).

Question 42

Why might observed phenotypes not match expected?

Answer 42

Fertilisation or gamete fusion is random.

Question 43

Another reason?

Answer 43

Small population or sample size.

Question 44

Genetic reason?

Answer 44

Selection advantage, disadvantage, or lethal alleles.

Question 45

What is the use of a Chi-squared test?

Answer 45

To test the significance of differences between expected and observed phenotypic ratios.