Topic 7A: Genetics

Question 1

What is monohybrid inheritance?

Answer 1

Inheritance of of a characteristic controlled by a single gene

Question 2

What is a gene?

Answer 2

a Sequence of bases on a DNA molecule that codes for a protein which results in a characteristic

Question 3

What is an allele?

Answer 3

Different versions of the same gene.

Question 4

What is a genotype?

Answer 4

The genetic constitution of an organism eg BB or Bb

Question 5

What is a phenotype

Answer 5

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

Question 6

What does dominant mean?

Answer 6

An allele whose characteristics appears in the phenotype even when there’s only one copy

Question 7

What does recessive mean?

Answer 7

An allele whose characteristic only appears in the phenotype of two copies are present

Question 8

What is codominance?

Answer 8

When both alleles are expressed

Question 9

What is locus?

Answer 9

A position of a gene on a chromosome.

Question 10

Give and example of codominance?

Answer 10

sickle cell anaemia

Question 11

What is sickle cell anaemia?

Answer 11

If the person has heterozygous phenotype its mean they have both normal Hb and some sickle Hb too. They are both equally expressed

Question 12

Name a gene that has multiple alleles

Answer 12

Your blood can be AA/AB/OO/OA/OB/BB

Question 13

What is the predicted phenotype ratio for monohybrid cross?

Answer 13

3:1

Question 14

What is the predicted phenotype ratio for dihybrid cross?

Answer 14

9:3:3:1

Question 15

What is the predicted phenotype ratio for codominance cross?

Answer 15

1:2:1

Question 16

Sometimes you wont get the expected phenotype ratios. Why?

Answer 16

due to
sex linkage
autosomal linkage or
epistatisis

Question 17

What does sex linked means?

Answer 17

when a characteristic’s allele is on a sex chromosome

Question 18

Which sex chromosome is smaller

Answer 18

Y

Question 19

Which sex chromosome carriers fewer genes

Answer 19

Y

Question 20

What is X linked?

Answer 20

When the allele is carried on the X chromosome

Question 21

Why are males more likely to show recessive phenotypes for genes that are sex linked?

Answer 21

Because males only have on X chromosome. The allele on that chromosome is therefore expressed even if it is recessive

Question 22

Name genetic disorders that are caused my faulty alleles on the sex chromosomes

Answer 22

Colour blindness (recessive)
haemophilia
(x-linked disorders)

Question 23

What are autosomes?

Answer 23

Chromosomes that are not sex chromosomes

Question 24

Autosomes are said to be linked…

Answer 24

if the genes are on the same chromosome

Question 25

What happens to autosomal chromosomes that are linked in meiosis?

Answer 25

They stay together during independent segregation

Their alleles are passed down to offspring

Question 26

Why might autosomal linked allele might not be passed down to offspring?

Answer 26

They might be separated by crossing over

Question 27

The closer together two genes are on the autosome…..

Answer 27

the more closely they are said to be linked

-This is because crossing over is less likely to split them