Genotype, Phenotype And Inheritance

Question 1

What is the different between the genotype and phenotype?

Answer 1

Genotype is the sequence of genes on chromosomes in the nucleus whereas the phenotype is the observable characteristics. The phenotype is influenced by both the genotype and the environment (eg radiation, lifestyle, chemicals, diet, lifestyle and mutagens)

Question 2

What is the difference between Hetrozygous and Homozygous?

Answer 2

Homozygous- Two alleles of a gene are the same (homozygote)

Heterozygous- two alleles of a gene are different. (Hetrozygote)

Question 3

What does it mean if an individual is hemizygous?

Answer 3

Only one alleles of a gene on the X chromosome.

MALES ONLY!

Question 4

What is the difference between a recessive and a dominant allele?

Answer 4

The dominant allele in a hetrozygote determines the phenotype (is expressed) whereas the recessive allele is not.

Question 5

What is Co-Dominance?

Answer 5

When neither allele in a heterozygote

are dominant over the other so, both are expressed in a phenotype. Eg blood type AB

Question 6

PEDIGREE DIAGRAMS

Answer 6

Remember to look over these!

Question 7

Discuss the autosomal recessive inheritance pattern

Answer 7

Heterozygotes are unaffected
Males and Females are equally effected
Two heterozygotes have 25% chance if having affected offspring
Two affected (homozygous) individuals will have affected offspring only.
Disease seem to ‘come out of nowhere’ because it can skip generations.
Eg cystic fibrosis

Question 8

Discuss the autosomal dominant inheritance pattern

Answer 8

Heterozygotes are affected.
Males and Females are equally affected
Diseases are rarely found in the homozygous state. (You can assume that an individual is heterozygous when it comes to diseased states because it is unlikely homozygous individuals would be viable for life)
Every affected individual has a 50% chance of having affected offspring and will have at least one affected parent.
Diseases cannot skip a generation.
Eg Huntington’s Disease.

Question 9

Discuss X linked recessive inheritance.

Answer 9

Hemizygous males and homozygous females affected.
Disease more common in males.
Heterozygous female ‘carrier’ has 50% chance of having affected sons.
Every affected make will have at least a heterozygous carrier mother.
Every affected female will have an affected father and a carrier mother
Affected males cannot give the trait to their sons but all their daughters will be heterozygous.
Eg Haemophilia A

Question 10

Discuss X linked dominant inheritance

Answer 10

Hemizygous males and heterozygous females affected.
Heterozygous affected female has 50% chance of having affected offspring.
Affected males cannot give train to sons but will give it to all their daughters.
Eg Retts syndrome

Question 11

Discuss Y linked inheritance

Answer 11

Only passed from father to son (and always passed on)

Also called holandric inheritance

Question 12

Discuss mitochondrial inheritance.

Answer 12

All individuals will inherit this from the mother as everybody gets mitochondria from maternal line.

Question 13

Discuss polygenic inheritance

Answer 13

Polygenic inheritance (as opposed to monogenic) is when more than one gene affects inheritance.
Genes on the same chromosome are said to be linked.
Linked genes go not show independent assortment at meiosis.
Recombination frequency between two linked genes is dependent on the distance between the genes. If they are closer, they are less likely to separate during crossing over (they are more ‘tightly linked’). If the genes are further apart then they almost behave as unlinked chromosomes.
Genes on different chromosomes are said to be not linked.