Inheritance And Pedigrees

Question 1

What is a genotype?

Answer 1

Your genetic make up

Question 2

What is a phenotype?

Answer 2

Physical characteristics

Question 3

What is the cycle of DNA?

Answer 3

DNA (nucleus), RNA (nucleus), proteins (cytoplasm).

Question 4

What is the difference between a gene and an allele?

Answer 4

A gene is a specific stretch of DNA that codes for a genotype e.g. Eye colour - we all have it. An allele is a variation of that gene e.g. Blue eyes, brown eyes. We all have the same genes but we all have different alleles for that gene.

Question 5

What is homozygous?

Answer 5

Where the two alleles of a gene are the same.

Question 6

What is heterozygous?

Answer 6

Where two alleles of the same gene are different.

Question 7

What is hemizygous?

Answer 7

Refers to X chromosome - having a gene where. Only one copy is present (in males only).

Question 8

What does dominant mean?

Answer 8

When the dominant allele determines the phenotype i.e. If you are a carrier of that allele then you have the disease.

Question 9

What does recessive mean?

Answer 9

The non-dominant allele. Have to have two copies of the allele to be affected.

Question 10

What is co-dominance?

Answer 10

Two alleles that are no dominant over one another e.g. In blood types, A and B have co-dominance.

Question 11

What shape is an unknown sex in a pedigree?

Answer 11

A diamond

Question 12

How can you tell someone is deceased in a pedigree?

Answer 12

They have a diagonal line through them from bottom left to top right.

Question 13

How can you describe the location of a person on a pedigree?

Answer 13

Use numbers (1,2,3) to determine which generation (going down) and roman numerals (I,II,III) to determine where in that generation (going from left to right).

Question 14

What is a heterozygote?

Answer 14

An individual who has two different alleles on one particular gene.

Question 15

Name four characteristics of autosomal recessive inheritance and one disease example.

Answer 15

Males and females equally affected
Can skip generations 
Can come 'out of nowhere'
Both parents must be carriers
Cystic fibrosis

Question 16

Name five characteristics of autosomal dominant inheritance and one example of a disease.

Answer 16

Males and females equally affected
Heterozygotes affected (if carrier then affected)
Does not skip generations
Rarely found in homozygous state - not viable for life
Every affected individual has a 50% chance of passing the trait on
E.g. Huntington’s disease

Question 17

Name six characteristics of x-linked recessive inheritance and a disease example.

Answer 17

More common in males
Hemizygous males and homozygous females affected
Heterozygous females have a 50% chance of passing the trait down to their son
Affected males cannot give trait to their sons
All affected daughters must have an affected father and a carrier mother
All daughters of affected males will at least be carriers
Haemophilia A

Question 18

Number three characteristics of x-linked dominant inheritance and a disease example.

Answer 18

Hemizygous males and heterozygous females affected
Affected females have a 50% chance of passing onto offspring
Males CANNOT give the trait to sons but WILL give the trait to daughters.
Marfans

Question 19

What is mitochondrial inheritance?

Answer 19

Mitochondrial DNA passed down only in mother so all individuals will inherit the trait from their mothers.

Question 20

What is Y-linked inheritance?

Answer 20

Very rare (Y chromosome is very small)
Only ever passed down from father to son

Question 21

What is monogenic inheritance?

Answer 21

Characteristic produced by a single gene or allele.

Question 22

What is polygenic inheritance?

Answer 22

Many genes involved in the expression of the trait (phenotype) e.g. Height and weight.

Question 23

What affects the probability of recombination on the same chromosome?

Answer 23

DISTANCE - gene close together are ‘tightly linked’ therefore recombination is more likely. Gene far apart are far less likely to recombine.