7.2 Genotype, Phenotype And Inheritance

Question 1

We know that the Genotype leads to the Phenotype. What affects both of these?

Answer 1

The environment - radiation, mutagens, lifestyle, diet, chemicals

Question 2

What is a gene?

Answer 2

Sequence of nucleotides forming part of a chromosome

Question 3

How many copies of a particular gene does an individual have and where from? What is different about them?

Answer 3

2 copies of each gene, one maternal and one paternal
Different alleles

E.g. Everyone has the protooncogene, its just whether the allele says it is active or not determines chances of cancer

Question 4

Definition of homozygous, heterozygous, hemizygous

Answer 4

Homozygous - two alleles of a gene are the same
Heterozygous - two alleles of a gene are different
Hemizygous - only one allele of a gene on X chromosome (boys)

Question 5

Definition of dominant and recessive

Answer 5

Dominant - this allele determines phenotype

Recessive - both alleles (maternal and paternal) have to be the same for phenotype to show

Question 6

Define codominance. Give an example.

Answer 6

Both alleles (maternal and paternal) of a gene are fully expressed with neither one being dominant or recessive to the other.

E.g. Blood type AB

Question 7

Describe autosomal dominant inheritance. Use:

Who is affected?
Gender?
Chance of affecting offspring?
Affected childs Parents affected? 
Generation?
Extra.

Answer 7

1. Heterozygous affects
2. Male and female equally affected
3. 50% chance of affecting offspring
4. At least one affected parent
5. Disease cannot skip a generation
6. Diseases rarely found in homozygous state as not viable for life

Question 8

Describe autosomal recessive inheritance. Use:

Who is affected?
Gender?
Chance of affecting offspring?
Affected childs Parents affected? 
Generation?
Extra.

Answer 8

1. Homozygous recessive, heterozygotes not affected
2. Male and females equally
3. 25% chance if both parents carriers
4. Both parents have to be atleast heterozygous carriers
5. Skip generations “comes out of nowhere”
6. Two homozygotes will have affected offspring only

Question 9

Describe X linked recessive inheritance. Use:

Who is affected?
Gender?
Chance of affecting offspring?
Affected childs Parents affected? 
Generation?
Extra.

Answer 9

1. Hemizygous males XnY and homozygous females XnXn
2. Disease more common in males
3. Affected males cannot give to sons, but defo makes daughters carriers
4. Every affected male has at least a carrier mother, every affected female has atleast affected father and carrier mother
6. Affected males will have heterozygous daughters

Question 10

Describe X linked dominant inheritance. Use:

Who is affected?
Gender?
Chance of affecting offspring?
Affected childs Parents affected? 
Generation?
Extra.

Answer 10

1. Hemizygous males and heterozygous females
3. Heterozygous female has 50% chance of passing on to offspring, hemizygous male cant give the trait to son, WILL give to all daughters
4. If cant see trait in father, mother is defo a carrier
   5.
   6.

Question 11

Describe Y linked inheritance. Use:

Who is affected?
Gender?
Chance of affecting offspring?
Affected childs Parents affected? 
Generation?
Extra.

Answer 11

1. Only males
3. Passed from father to sons, cant pass on to daughters
4. Father has to be affected to pass on
5. Doesn’t skip
6. Y chromosome is small so rare!

Question 12

Describe mitochondrial inheritance. Use:

Who is affected?
Gender?
Chance of affecting offspring?
Affected childs Parents affected? 
Generation?
Extra.

Answer 12

1. All individuals from affected mother
2. Both depending on Tree
3. If mother has, all children will have. Father cannot pass on.
4. Mother has to be affected
5. Doesn’t skip generations

Question 13

What is polygenic inheritance?

Answer 13

More than 1 gene is involved in a phenotype.

E.g. Albinism - if both parents affected, you expect all children to be affected (as autosomal recessive). But this is not true! 4 genes affect albinism. It may be that mothers defective allele compensated for by fathers working allele for that gene, and another that is defective in father, is compensated for by a working allele in the mother.

Question 14

What is complementation?

Answer 14

1 allele in a gene (e.g. Mothers) compensates for a mistake in other allele in that gene (father)

Question 15

What is it called when genes are on the same chromosome?
What is it called when genes are on different chromosomes?
What is a feature of the first type?

(3)

Answer 15

1. Linked
2. Not linked
3. Do not show independent assortment at meiosis as you cant split up a chromosome! These genes will move into the next cell together (unless Chiasma)

Question 16

What is meant by two genes being tightly linked? What are the consequences of this?

Answer 16

Two genes are very close together on arm of chromosome

They are less likely to be seperated by chiasmata as they’re very close and prob will move together

Question 17

What is meant by two genes being unlinked? What are the consequences of this?

Answer 17

Two genes not very close on arm of chromosome and more likely to be seperated via chiasmata as opposed to tightly linked genes

Question 18

What is genotype and phenotype?

Answer 18

Genotype is the alleles an individual has at a locus (position of gene) on a chromosome

Phenotype is the visible expression of the genotype