Genes and patterns of inheritance

Question 1

What is a gene?

Answer 1

Short sections of DNA that code for a particular polypeptide

Question 2

What is an allele

Answer 2

A particular form of a gene

Question 3

What is the gene locus?

Answer 3

The position of the gene on a locus

Question 4

What is Mendels law of segregation?

Answer 4

Two alleles of the same gene separate during meiosis with only one entering each gamete

Question 5

What is a genotype

Answer 5

Two alleles for a particular characteristic

Question 6

What is a phenotype?

Answer 6

The outward appearance of the individual in terms of the trait under consideration

Question 7

What is dominance?

Answer 7

In heterozygous condition the dominant allele will override the recessive allele

Question 8

What is recessive?

Answer 8

The recessive allele will be dominated by the dominant allele

Question 9

How do you do a test cross?

Answer 9

Cross the unknown individual with homozygous recessive and the ratio of phenotype will tell you the genotype of the unknown

Question 10

What is co dominance?

Answer 10

1:2:1 ratio is observed when two heterozygote parents are crossed for a trait that displays co-dominance

Question 11

What is observed for multiple alleles e.g. blood groups

Answer 11

blood groups shows 1:1:1:1

Question 12

What is a ratio of 2:1 an example of

Answer 12

2:1 is an example of a lethal allelic combination. The offspring that have the lethal allelic combination will fail to develop as embryos and you will not see the phenotype. Only non lethal combinations will be able to be counted

Question 13

what does it mean for a trait to be sex linked?

Answer 13

For a trait to be sex linked there is a close correlation between the trait and sex of the individual

Question 14

Why do males generally have the disease

Answer 14

The Y chromosome is described as being genetically empty. The males only have one X chromosome so if they have the recessive allele they will have the disease. Females can have the recessive and the dominant and will therefore be a carrier for the disease

Question 15

For a male baby to have the disease what must happen

Answer 15

The mother has to be a carrier as he inherits his X chromosome from his mother and Y from his father

Question 16

What is a carrier

Answer 16

Someone who carries the allele but is phenotypically normal

Question 17

What will happen if a sex linked disease is present in both parents and is dominant?

Answer 17

It will be seen in all offspring

Question 18

For a pedigree diagram what indicates that it is :

1. Autosomal recessive
2. Autosomal dominant
3. X-linked recessive
4. X-linked dominant

Answer 18

1. Will only appear in some generations as it is hidden in others (autosomal = equal numbers of male and female)
2. Impossible to pass condition on without at least one parent having the trait (autosomal = equal male and female)
3. More common in males but not present in all
4. NOT mainly restricted to males. A Father will pass it to all of his daughters

Question 19

What is dihybrid inheritance?

Answer 19

Investing two traits together e.g. height and shape of peas

Question 20

What is 9:3:3:1

Answer 20

di hybrid inheritance

Question 21

What is Mendels second law?

Answer 21

The law of independent assortment -
During the formation of gametes the segregation of the alleles of one gene is independent of the segregation of alleles of another gene

Question 22

Where does mendels second law occur ?

Answer 22

Occurs at bivalents during metaphase 1

Question 23

What are the two main types of ratios for dihybrid inheritance and how do they come about?

Answer 23

9:3:3:1 and 1:1:1:1
Their ratios are classified as dihybrid inheritance when each of the two genes involved has a dominant and recessive allele

Question 24

What is independently inherited?

Answer 24

When the genes are on different chromosomes

Question 25

What is polygenic inheritance, ratio

Answer 25

1:4:6:4:1

The additive effect of more than two genes. There is continuous variation

Question 26

What is the 15:1 ratio an example of ?

Answer 26

Epistasis where only one of the two genes is necessary to produce a particular phenotype

Question 27

What is the 9:3:3 ratio an example of ?

Answer 27

Epistasis with a lethal allele combination

Question 28

What is epistasis?

Answer 28

Where one gene interferes with the expression of another

Question 29

What is the 9:7 ratio

Answer 29

Epistasis where at least one dominant allele must be present in each gene. Two genes are necessary to produce a particular phenotype

Question 30

what is 12:3:1

Answer 30

Dominant epistasis where one allele of a gene blocks the expression of both alleles of another gene

Question 31

what is 9:3:4

Answer 31

Recessive epistasis where homozygous state of one gene blocks the expression of both alleles of another gene

Question 32

What is epigenetics?

Answer 32

The role of the environment in affecting gene expression. Some genes can be turned off in the first place

Question 33

Why is mendels research considered reliable?

Answer 33

Large number of replicates