Patterns of Inheritance

Question 1

What is Gene Linkage/Linkage?

Answer 1

When two or more genes are located on the same chromosome

Question 2

What is autosomal linkage?

Answer 2

Linked genes which are on non sex chromosomes

Question 3

What is sex linkage?

Answer 3

Linked genes which are on sex chromosomes - Therefore specific characteristics are more likely to be inherited in either male or female offspring

Question 4

Why are Linked Genes more likely to be passed on together?

Answer 4

Since their loci are close together on the chromosome

Question 5

In sex linkage, genes are more likely to be what?

Answer 5

X-linked (found on X chromosome)

Question 6

If Sex-Linked genes are X-linked, what does this mean for female and male offspring? Give a real life example.

Answer 6

• It means female offspring will only show recessive genes if homozygous
• Male offspring will show recessive X-linked genes even if only present on X chromosome
  E.g. Colour blindness is more common in males

Question 7

What is Epistasis?

Answer 7

The interaction of non-linked genes where one masks the expression of the other

Question 8

What is Recessive epistasis? Give an example.

Answer 8

Homozygous recessive alleles mask expression of another allele at a different locus

E.g. flower colour in Salvia

• Two Gene loci : A/a, B/b
• B= purple; b = pink; a = white
• Plant with genotype AABB is purple
• Plant with genotype AAbb is pink
• But any plant with genotype aa – will be white - even if alleles at B/b are homozygous dominant
• Homozygous aa is epistatic to both alleles of the B/b gene (Neither B nor b is expressed at least one dominant A is present)

Question 9

What is Codominance?

Answer 9

When both alleles present in the genotype contribute to the phenotype

Question 10

Give an example of allele co-dominance

Answer 10

Human blood groups

• Individual possessing A allele, with or without O allele, expresses blood type A. Same with B
• If individual has A and B – Expressed AB blood type

Question 11

What is meant by the term genotype?

Answer 11

Genetic makeup of an individual

Question 12

What is meant by the term phenotype?

Answer 12

The visual characteristic of the individual

Question 13

Genetic variation is caused by mutations. What three things can these mutations be caused by? Give 2 examples of each.

Answer 13

Mutagenic agents E.g.
- X-rays/Gamma rays
- Viruses
Chromosomal mutations E.g
- Deletion: nucleotides deleted, part of chromosome lost
- Inversion: section of chromosome breaks off, and is reinserted in the opposite direction
Normal sexual reproduction
- Meiosis produces genetically different gametes
- alleles shuffle around
- Independent assortment of chromosomes
- Contribute to genetic diversity
- Random fusion of gametes at fertilisation

Question 14

What is Aneuploidy?

Answer 14

Where the chromosome number is not a multiple of the haploid number for that organism

Question 15

What is Polyploidy?

Answer 15

A diploid gamete is fertilised by a haploid gamete = resulting zygote is triploid

Question 16

Phenotypic factors of variation include what two things?

Answer 16

• Variation caused by the environment alone
  E.g. losing a limb in an accident
• Variation caused by the environment interacting with genes

Question 17

What is Epigenetics?

Answer 17

Variation caused by the environment interacting with genes, environmental conditions can effect the expression of genes.

Question 18

How does Epigenetics work?

Answer 18

Genes are put in certain ‘modes’ where they might behave in a certain way E.g. plants reacting to light

Question 19

How is Epigenetics passed?

Answer 19

Vertically - From parent to offspring

Question 20

What is Discontinuous variation?

Answer 20

- Phenotypes are in distinct categories
  E.g. blood type/sex, can’t be ‘between’ A and B
- Determined by a single allele
- Monogenic
- Qualitative

Question 21

What is Continuous variation?

Answer 21

• Phenotypes fall in a range
• Smooth gradient between phenotypes
• E.g. mice tail length; birth weight; height; skin colour
• Controlled by more than one gene
• Polygenic
• Quantitative