Genetics And Inheritance

Question 1

What is a genotype

Answer 1

The genetic constitution of an organism. All the alleles that an organism possesses.

Question 2

What is a gene pool

Answer 2

All the alleles within an interbreeding population at a specific time

Question 3

What is a phenotype

Answer 3

The expression of the genotype and its interaction with the environment (e.g.physical appearance)

Question 4

What is an allele

Answer 4

Different versions of the same gene. Can be dominant, recessive or codominant

Question 5

Homozygous

Answer 5

Same allele

Question 6

Heterozygous

Answer 6

Different alleles

Question 7

Define dominant allele

Answer 7

It is ALWAYS expressed in the phenotype

Question 8

Define recessive allele

Answer 8

Only expressed in the phenotype if the genotype is HOMOZYGOUS

Question 9

Codominant allele

Answer 9

Equally expressed within the phenotype

Question 10

What does the hardy Weinberg principle state

Answer 10

The alleles frequency will remain constant from one generation to the next if :
- mating is random
- there is no mutations
- there is a large population
- zero migration
- no change in selection pressures

Question 11

What does allelic frequency mean

Answer 11

The number of times an allele occurs in a gene pool

Question 12

In the hardy Weinberg principle what is the letter for the dominant allele

Answer 12

P

Question 13

What is the letter that represents the recessive allele in the hardy Weinberg principle

Answer 13

q

Question 14

What are the 2 hardy Weinberg equations we need to know

Answer 14

P + q = 1

P2 + 2Pq + q2 = 1

Question 15

What is monohybrid inheritance

Answer 15

The inheritance of a single gene which determines a single characteristic

Question 16

Gene expression is

Answer 16

…which protein is being synthesised

Question 17

What is a gene

Answer 17

A gene is a section DNA that codes for a specific protein

Question 18

Ratio for monohybrid inheritance

Answer 18

3:1

Question 19

Ratio for codominance

Answer 19

1:2:1

Question 20

Rules for dominant and recessive

Answer 20

Dominant:
Unaffected parents can only have unaffected offspring
Affected offspring must have at least one affected parent
If both parents are unaffected and produce an affected offspring both parents must be heterozygous

Recessive:
Unaffected parents can have affected offspring if they are heterozygous

Question 21

Sex linage rules

Answer 21

Dads and daughters (recessive):
If daughter is affected (homozygous recessive)
And Her father is not
And it is a recessive disease
It is not sex linked

Mums and sons (dominant):
If the son is affected
But the mother is not (homozygous recessive)
And it is a dominant disease
It is not sex linked

Question 22

What is dihybrid inheritance

Answer 22

Involves a phenotype that is inherited as a result of two genes so two different characteristics

Question 23

What is the ratio for dihybrid inheritance

Answer 23

9:3:3:1

Question 24

What is the ratio for epistasis

Answer 24

9:4:3
15:1
9:7
All add to 16 but dot show 9:3:3:1

Question 25

State three causes of genetic variation

Answer 25

• Mutation
• Crossing over
• Independent segregation / assortment (of homologous chromosomes)
• Random fusion of gametes / fertilisation / mating

Question 26

What is meant by a genome?

Answer 26

• (All) the DNA in a cell/organism;
• ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
• ‘the total number of DNA bases in a cell/organism’

Question 27

What is a gene pool?

Answer 27

• All the alleles in a population;

Question 28

How do multiple alleles of a gene arise?

Answer 28

• mutations;
• which are different / at different positions in the gene;

Question 29

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Suggest two reasons why.

Answer 29

• Small sample size;
• Fusion/fertilisation of gametes is random;
• Linked Genes; Sex-linkage / crossing over;
• Epistasis;
• Lethal genotypes;

Question 30

What is meant by a recessive allele?

Answer 30

• Only expressed in the homozygote / not expressed in the heterozygote / not expressed if dominant present;1

Question 31

What does Hardy Weinberg’s equation predict

Answer 31

• The frequency/proportion of alleles (of a particular gene);
• Will stay constant from one generation to the next/over generations / no genetic change over time;
• Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration;

Question 32

Define epistasis

Answer 32

• The allele of one gene affects or masks the expression of another in the phenotype;

Question 33

Describe why observed phenotypes don’t match expected values

Answer 33

• Fertilisation is random
• OR
• Fusion of gametes is random;
• Small/not-large population/sample;
• Selection advantage/disadvantage/lethal alleles;

Question 34

Define codominance

Answer 34

• Both alleles expressed in the phenotype;

Question 35

Rules for Dominant alleles

Answer 35

• Affected offspring MUST have at least one affected parent.
• Unaffected parents ONLY have unaffected offspring.
• If both parents are affected and have an unaffected offspring, both parents must be Heterozygous

Question 36

Rules for recessive alleles

Answer 36

• Unaffected parents can have an affected offspring (if they are Heterozygous)

Question 37

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.

Answer 37

• (Recessive) allele is always expressed in males / males have one (recessive) allele;
• Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;

Question 38

Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage

Answer 38

Dominant : recessive

1. 3:1
2. 9:3:3:1
3. 9:4:3 or 15:1 or 9:7
4. 3:1 (no x over) (no other pattern other than 4 phenotypes with recombination of alleles)

Question 39

What is meant by the term phenotype

Answer 39

• (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s);

• (Expression / appearance / characteristic due to) interaction with environment;

Question 40

Explain how a single base substitution causes a change in the structure of a polypeptide

Answer 40

• Change in (sequence of) amino acid(s)/primary structure;
• Change in hydrogen/ionic/disulfide bonds;
• Alters tertiary/30 structure;