Genotype, Phenotype And Inheritance

Question 1

What is genotype?

Answer 1

Is the alleles present

Question 2

What is the phenotype?

Answer 2

Observable characteristics

Question 3

What effects genotype and phenotype?

Answer 3

Genotype can be effected by the environment - e.g. radiation, mutagens, chemicals that alter DNA
Phenotype is effected by genotype and can be the environment - e.g. diet, lifestyle,smoking

You may be more likely genetically to get cancer and then increase risk by smoking

Question 4

What is the difference between a gene and an allele ?

Answer 4

A gene is a section of DNA that codes for a protein. So everyone had the same genes. Alleles are version of the same genes. So there are many alleles for one gene. Each individual has 2 alleles of the same gene (one from each parent)

Question 5

What does homozygous mean?

Answer 5

The 2 alleles are the same

Question 6

What is someone who is homozygous for a gene called?

Answer 6

A homozygote

Question 7

What does heterozygous mean?

Answer 7

Two alleles of a gene are different

Question 8

What does hemigzygous mean ?

Answer 8

In males only, when there is only one allele of a gene on the X chromosome because is it not on the Y chromosome.

Question 9

What is it called when someone has only one allele of a gene on the X chromosome?

Answer 9

Hemizygous

Question 10

What does dominant mean?

Answer 10

The allele is always expressed

Question 11

What does recessive mean ?

Answer 11

The allele is only expressed when homozygous

Question 12

What is it is called when 2 alleles are both expressed ?

Answer 12

Co-dominance

Question 13

What are the human blood groups ?

Answer 13

3 alleles A,B,O. A and B are co-dominant and o is recessive. Blood groups are A, B, AB, O. Blood group O has no antigen.

Question 14

What are the potential genotypes of the phenotype blood group A

Answer 14

Could be IAIA or IAIO

Question 15

In pedigree trees what do the following mean;
White/black
Square/circle
Half coloured
Diamond 
Line through the shape

Answer 15

White=uneffected
Black=effected
Square=male
Circle=female
Half coloured=carrier
Diamond=unknown sex
Line through=dead

Question 16

Describe autosomal recessive

Answer 16

Single gene where you must have 2 of the allele to be effected. 
Make and females equally effected
Disease can skip generations 
Both parents of affected are carriers 
E.g. cystic fibrosis

Question 17

Draw a punette square to show mating of 2 carriers for a recessive condition. What are offspring phenotype and genotypes

Answer 17

AA normal
Aa normal
aA normal (can write this the other way round)
aa affected

Question 18

Describe autosomal dominant

Answer 18

Need only 1 allele copy to be effected.
Makes and females affected equally
Not normally homozygous (as normally killed so if it says its dominant and the person has it presume they are heterozygous)
E.g. Huntington’s disease
Effected individual will have at least one affected parent
Will not skip a generation

Question 19

Describe X linked recessive inheritance

Answer 19

Hemizygous makes and homozygous females are affected.
More common in makes (only get one X chromosome so that x will always be expressed)
Males cannot give trait to sons- because passed on the X gene and male alleles only have a Y chromosome
Male and female are unequally effected (sex linked)
E.g. haemophilia

Question 20

Find out what the genotype and phenotype of the offspring of an affected male and carrier female.

Answer 20

1 carrier female
1 affected female
1 healthy male
1 affected male

Question 21

Where is mitochondrial DNA inherited from?

Answer 21

Mother only

Question 22

Can inheritance be of more than one gene?

Answer 22

Yes it’s called polygenic inheritance

Question 23

Describe polygenic inheritance

Answer 23

Sometimes several genes are involved in the production of a phenotype. One gene could produce a substrate that needs several enzymes to transform it into the product. These enzymes require other genes to code for them.

Question 24

You should always assume when working with inheritance that it is v complicated polygenic inheritance.
True or false

Answer 24

No always use the most simple single gene inheritance model first (monogenic)

Question 25

If working with the inheritance of 2 genes and a parent has the genotype aaBB what are the gametes

Answer 25

aB as the gametes need one allele of each gene

Question 26

Explain and describe linked genes.

Answer 26

Genes on the same chromosome are linked. Genes on different chromosomes are not linked.
Linked genes do not independently assort at meiosis (so they’re inherited together).

Question 27

How does recombination frequency relate to linked genes?

Answer 27

The further the distance between the genes the less tightly linked and so the less likely they are to be inherited together