Genotype, Phenotype And Inheritance

Question 1

What is a genotype?

Answer 1

The genes a person has on the chromosomes in their nucleus

Question 2

What is a phenotype?

Answer 2

The proteins a person has on their cytoplasm

Question 3

What can effect genotype and phenotype?

Answer 3

Environment
Chemicals 
Diet 
Mutagens 
Lifestyle 
Radiation

Question 4

What are alleles?

Answer 4

Different copies of the same gene

Question 5

Define Homozygous

Answer 5

2 alleles of a gene are the same

The individual is a homozygote

Question 6

Define Heterozygous

Answer 6

2 alleles of a gene are different

Individual is a heterozygote

Question 7

Define Hemizygous

Answer 7

Only one allele of a gene

Eg one allele as only one X gene as male

Question 8

Define dominance in inheritance

Answer 8

The dominant allele in a heterozygote determines the phenotype

(Only one copy is needed)

Question 9

Define recessive in inheritance.

Answer 9

The non-dominant allele in a heterozygote is called recessive

Need 2 copies to appear in phenotype

Question 10

Give an example of Co-Dominance

Answer 10

Human iso-glutamin gene codes for the glycoproteins on RBC surface. These are co-dominant and 2 can be present in phenotype.

A is dominant over O
B is dominant over O
A and B are co-dominant so appear together

Question 11

How is a male and female represented in a pedigree chart?

Answer 11

Male=square
Female=circle
Unknown sex=diamond

Question 12

How do you represent an effected/unaffected/carrier in a pedigree chart?

Answer 12

Affected=coloured in
Unaffected=not coloured
Half and half = carrier

Question 13

How do we label different generations in a pedigree chart?

Answer 13

Label each generation with a Roman numeral

Question 14

Describe the features of an autosomal recessive gene

Answer 14

Heterozygotes are unaffected (as recessive)
Equal in both sexes (not sex-linked)
2 heterozygote have 25% chance effected offspring
2 affected divide all can only have affected children

Question 15

Give an example of an autosomal recessive genetic disease

Answer 15

Cystic Fibrosis

Question 16

Describe the features of an Autosomal Dominant genetic disease.

Answer 16

Heterozygotes effected (1 copy needed)
Both sexes equally affected
Disease rarely found in homozygous state as not viable for life
If affected - 50% chance of affected offspring
Cannot skip a generation
An affected individual has at least one affected parent

Question 17

Give an example of an autosomal dominant genetic condition

Answer 17

Huntington’s disease

Question 18

Describe the features of an X-lined recessive genetic condition

Answer 18

Hemizygous males affected
Homozygous females affected
More common in males
Heterozygous female (carrier) has 50% chance of affected son
Affected male cant pass it on to SONS (as give them the Y gene)

Affected Male must have (at least) heterozygous carrier mother
Affected female must have affected father + carrier mother
Daughter of affected male must be carrier

Question 19

Give an example of an X-linked recessive genetic condition

Answer 19

Haemophilia A

Question 20

Describe the features of an X-Linked Dominant genetic condition

Answer 20

Hemizygous male affected
Heterozygous female affected
Affected male cant pass it to sons but will to ALL daughters

Question 21

Give an example of X-Linked dominant genetic condition

Answer 21

Fragile X syndrome

Question 22

Describe some feature of Y-Linked genetic diseases

Give an example

Answer 22

An effected mans sons will all get it
Females cant get it
Passes from father to son

Eg Y-Chromosome infertility

Question 23

Describe the features of mitochondrial genetic conditions

Answer 23

Must be inherited from mother

Given to all of an affected woman’s children
Boys cant pass it on

Question 24

What is polygenic inheritance

Answer 24

When the inherited disease is formed by more than one gene there are more than one possible genetic mutations

Genes on same chromosome said to be linked
Genes on diff chromomes “not linked”

Linked genes don’t show independent assortment at meiosis

Question 25

Give Na example of a disease for poly genetics

Answer 25

Albinism

Question 26

What is the effect of linked and not linked on polygenic inheritance

Answer 26

Not linked-can be independently assorted-4 types of gamete with 1:1:1:1 ratio

Linked-can have crossing over (if no crossing over only 2 gametes, if crossing over 4) the ratios are not 1:1 if crossing has occurred. The ratio of the last 2 depend on how much crossing over occurs.

Question 27

What is recombination frequency between 2 genes dependant on

Answer 27

The distance between them

If close they are tightly linked (more likely to stay together)

If far apart they almost behave as unlinked genes, the further apart the more likely they are to cross over