7.1 Inheritance

Question 1

What is a genotype?

Answer 1

The genes that an organism has

Question 2

What is phenotype?

Answer 2

The observable characteristics of an organism

Comprised of the genotype and environmental factors

Question 3

What is a dominant allele?

Answer 3

Only one allele is required for the characteristic to be expressed in the phenotype

Question 4

What is a recessive allele?

Answer 4

The characteristic is only expressed in the absence of a dominant allele

2 alleles are required for the phenotype to be expressed

Question 5

What is a co-dominant allele?

Answer 5

Both alleles are expressed equally and contribute to the phenotype

Either a blend or both are shown

Question 6

What does pure breeding mean?

Answer 6

You breed a homozygous pair of alleles

Question 7

What is an allele?

Answer 7

A version of a gene

Question 8

What is homozygous and heterozygous?

Answer 8

Homozygous - same type of allele

Heterozygous - different types of alleles

Question 9

What is the locus?

Answer 9

The specific position of the gene on a chromosome

Question 10

What are homologous pairs?

Answer 10

The have the same genes but different alleles

Question 11

What do we use to workout the offspring phenotypes and genotypes?

Answer 11

Genetic cross diagram

Question 12

What is monohybrid inheritance?

Answer 12

A phenotype is controlled by a single

1 gene - 1 characteristic - 2 alleles

Question 13

In monohybrid inheritance what are the ratios for F(0) and F1 of homozygous dominant and homozygous recessive crosses?

Answer 13

1

And

3:1 (this is from crossing the genotypes of the first cross)

Question 14

What is dihybrid inheritance?

Answer 14

When two characteristics are studied and is determined by two different genes that are present on two different chromosomes at the same time

2 genes - 2 characteristics - 2 chromosomes

Question 15

What gametes can you have from these two examples in dihybrid inheritance?
RRGG
RrGg

Answer 15

RRGG = RG

RrGg = RG Rg rG rg

Question 16

What is codominance?

Answer 16

Both alleles in a heterozygous organism are equally dominant and are both expressed in the phenotype

2 alleles dominant

Question 17

What is an example of codominance for red colour and white colour? F0
Genotypes?
Gametes?
Offspring?

Answer 17

Genotypes = C^RC^R and C^WC^W (C is used for colour)

Gametes = C^R C^R C^W C^W

Offspring = C^RC^W = pink 100%

Question 18

What is an example of codominance for red colour and white colour? F1 (second cross)
Genotypes?
Gametes?
Offspring?

Answer 18

Genotypes = C^RC^W and C^RC^W (C is used for colour)

Gametes = C^R C^W C^R C^W

Offspring
C^RC^R = red 25%
C^RC^W = pink 50%
C^WC^W = white 25%

Question 19

What is multiple alleles?

Answer 19

More than 2 alleles for 1 gene

Look for supercripts

Question 20

Example of multiple alleles?

Answer 20

Blood groups

Question 21

What do the alleles of the blood groups produce? (co-dominance example)

Answer 21

I referring to Gene I (immunoglobulin gene)

I^A = antigen A
I^B = antigen B
I^O = produces neither A or B

A and B are co-dominant
O is recessive

Question 22

What are the combinations of blood groups?

Answer 22

Blood Group A
I^AI^A or I^AI^O

Blood Group B
I^BI^B or I^BI^O

Blood Group AB
I^AI^B

Blood Group O
I^OI^O

Question 23

What is sex linkage?

Answer 23

The expression of an allele dependent on the gender of the individual
(As the gene is located on a sex chromosome)

Look for father-daughter relationships in pedigree charts (often on X)

Question 24

What are the sex chromosomes in humans?

Answer 24

Male - XY

Female - XX

Question 25

What is significant about sex linked traits?

Answer 25

Most are located on the X chromosome
Because there is no equivalent locus on the Y chromosome

(The X chromosome is double the size)

Question 26

What should you be weary of with sex linkage?

Answer 26

That animals probably won’t be represented by X and Y sex chromosomes

Question 27

What is an example of a sex linkage?

Answer 27

Haemophilia

Blood clots slowly can lead to slow internal bleeding

Question 28

What are some genetic facts of haemophilia?

Answer 28

Male affected X^hY
Female affected X^hX^h
=Recessive h

Carried by the X chromosome
If a boy is born the X has to come from the mother
She can be a carrier without having it

Question 29

What is an autosome?

Answer 29

All the non sex chromosomes

= 44 in humans

Question 30

What is autosomal linkage?

Answer 30

Two or more genes are on the same autosomal chromosome

They are linked and stay together during independent segregation in meiosis = inherited together

Question 31

In autosomal linkage if you have two homologous pairs (4 chromosomes paired) what is the result of the gametes?

Answer 31

They will have 4 different types of gametes

1st pair of chromosomes = AA and aa
2nd pair of chromosomes = BB and bb

= AB Ab aB ab

Question 32

In autosomal linkage if you have one homologous pair (2 chromosomes paired) what is the result of the gametes?

Answer 32

There will be 2 different types of gamete

1st chromosome in the pair
= AA BB

2nd chromosome in the pair
= aa bb

= AB and ab

Question 33

Where can autosomal linkage be different?

Answer 33

If crossing over takes place different gametes will form

Question 34

What is significant about the closeness of loci on genes?

Answer 34

The more closely linked they are

Question 35

What happens in Epistasis?

Answer 35

One gene locus affects the other gene locus

One gene loci can either mask or suppress the expression of another gene locus

2 genes leading to one characteristic (1 gene can mask the expression of the other)

Question 36

What happens in recessive epistasis?

Answer 36

When a recessive allele prevents the expression of another allele at the second locus

Ratio - 9:3:4

Question 37

What happens in dominant epistasis?

Answer 37

When a dominant allele at one locus completely masks the alleles at the second locus

Ratio - 12:3:1