Topic 18 - Inherited Changes

Question 1

Define allele.

Answer 1

One different form of the same gene located at a specific position on a specific chromosome.

Question 2

Define homologous chromosome

Answer 2

Pair of chromosomes that have same gene loci and determine same features - not identical.

Question 3

Define homozygous dominant

Answer 3

Organism with two dominant alleles

Question 4

Define nucleotide

Answer 4

Organic compound made up of nitrogenous base, a sugar, and a phosphate group.

Question 5

Define homozygous recessive

Answer 5

Organisms with two recessive alleles.

Question 6

Define chromosome

Answer 6

Structure within nucleus of eukaryotic cells that bear genetic material as a threadlike linear strand of DNA bonded to histone proteins.

Question 7

Define gene

Answer 7

A section of DNA that determines a single characteristic of an organism.

Question 8

Define gamete

Answer 8

A reproductive sex cell that fuses with another gamete during fertilisation.

Question 9

Define co-dominance

Answer 9

Both alleles contribute to the phenotype

Question 10

Define fertilisation

Answer 10

Nucleus of a sperm cell fuses with nucleus of an ovum. Fusion of these gametes results in a zygote, which has 46 chromosomes. 23 inherited from mother, 23 inherited from father.

Question 11

What is monohybrid inheritance?

Answer 11

Inheritance of a single gene.

Question 12

What are expected ratios?

Answer 12

There are ratios of expected genotypes and phenotypes for each cross.
In practice this does not always happen - it’s down to chance.
The larger the sample, the more likely you are to find ratios closer to the theoretical value.

Question 13

What is dihybrid inheritance?

Answer 13

Explanation for how 2 characteristics are determined by 2 genes located on different chromosomes.

Question 14

What are multiple alleles?

Answer 14

Describes a situation when a gene has more than two alleles.

E.g. there are three alleles that are associated with the immunoglobulin gene I.
I^A
I^B
I^o

I^A and I^B are co-dominant
I^o is recessive to both

Question 15

Why is sex inheritance (sex linkage) ‘unlike’ other features of inheritance?

Answer 15

Sex is determined by a chromosome, not a gene.

Question 16

Which gender are sex linked characteristics most likely to appear in?

Answer 16

Males as the X chromosome carried the allele. Males only have one X chromosome so only need one recessive allele, females have two X chromosomes so need two recessive alleles. The Y chromosome doesn’t carry an allele.

Question 17

What is a pedigree chart?

Answer 17

Used to trace the inheritance of characteristics, which can be sex-linked or not.

Question 18

What is autosomal linkage?

Answer 18

Two genes are on the same chromosome and gametes are no longer produced in equal proportions.

Question 19

What is epistasis?

Answer 19

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