Genetics

Question 1

What chemical are chromosomes and genes made from?

Answer 1

DNA

Question 2

Put the following biological structures in size order starting with the largest: cell, chromosome, DNA, nucleus, gene

Answer 2

cell → nucleus → chromosome → gene → DNA

Question 3

The allele for brown eyes (B) is dominant over the allele for blue eyes (b).

What colour eyes would these people have:

BB
Bb
bb

Answer 3

The people with BB and Bb would have brown eyes because a dominant allele is always expressed (even if only 1 copy is present).

The person with bb would have blue eyes because a recessive allele is only expressed when 2 copies are present (no dominant allele).

Question 4

Which one of these people is heterozygous:

BB
Bb
bb

Answer 4

Bb because the 2 alleles are different.

Question 5

Which of these people are homozygous:

BB
Bb
bb

Answer 5

BB and bb because the 2 alleles are the same.

Question 6

The allele for brown eyes (B) is dominant over the allele for blue eyes (b).

A woman has blue eyes.

What are the woman’s alleles?

Answer 6

bb because the allele for blue eyes is recessive and a recessive allele is only expressed when 2 copies are present.

Question 7

How many chromosomes does an ordinary human body cell contain?

Answer 7

46 / 23 pairs

Question 8

What is a gene?

Answer 8

A small section of DNA on a chromosome.

Codes for a specific protein.

Question 9

Describe the structure of DNA

Answer 9

Made of 2 strands which twist around each other to form a double helix

Question 10

What are chromosomes?

Answer 10

Long pieces of DNA.

Found in the nucleus of cells.

Carry many genes.

Normally found in pairs (one from each parent).

Question 11

What are alleles?

Answer 11

Different versions of the same gene i.e. you have a gene for eye colour but there are versions which give blue eyes and versions which give brown eyes.

Question 12

What is the difference between a dominant allele and a recessive allele?

Answer 12

A dominant allele is always expressed even if only one copy is present.

A recessive allele is only expressed if 2 copies are present (no dominant allele).

Question 13

Define homozygous.

Answer 13

2 alleles for a particular gene are the same e.g. BB or bb.

Question 14

Define heterozygous.

Answer 14

2 alleles for a particular gene are different e.g. Bb.

Question 15

Define genotype.

Answer 15

The genes / alleles a living organism has.

Question 16

Define phenotype.

Answer 16

A living organisms characteristics (physical features).

Question 17

Give the combination of sex chromosomes present in a male and a female.

Answer 17

Male XY
Female XX

Question 18

Draw a genetic diagram to show sex inheritance.

Answer 18

Chance of male offspring = 50 %
Chance of female offspring = 50 %

Question 19

What is DNA?

Answer 19

A chemical that holds the genetic material (the code for making proteins).

Contained in structures called chromosomes.

Question 20

Give characteristics which are the result of the genes a living organism has inherited from its parents.

Answer 20

Characteristics which you are born with and can’t change.

Blood group
Eye Colour
Earlobe shape

Question 21

Give characteristics which are the result of the conditions in which an organism has developed (environmental).

Answer 21

Scar
Language
Accent

Question 22

What is a mutation?

Answer 22

A change in the DNA.

Question 23

Give characteristics which are the result of both the genes an organism has inherited from its parents and the conditions in which the organism has developed (environmental).

Answer 23

Skin colour
Weight
Height

Question 24

What is cell division?

Answer 24

Parent cell divides to produce two genetically identical cells.

Question 25

Why is cell division important?

Answer 25

Growth
Repair

Question 26

What has to happen before a cell divides?

Answer 26

DNA replicates to form 2 copies of each chromosome.

Question 27

A human cell cells divides to produce two genetically identical cells.

How many chromosomes are there in each new cell?

Answer 27

46 or 23 pairs

Question 28

The allele for brown eyes (B) is dominant over the allele for blue eyes (b).

A man with alleles Bb and woman with the alleles Bb plan to have a child.

What is the chance the child will have:

a) brown eyes
b) blue eyes

Answer 28

a) BB, Bb and Bb all have brown eyes so a 75 % chance of the child having brown eyes.
b) bb has blue eyes so a 25 % chance of the child having blue eyes.

Question 29

Polydactyl is an inherited disorder.

The allele for having polydactyl is dominant (D).

The allele for not having polydactyl is recessive (d).

A man with the alleles DD and woman with the alleles dd plan to have a child.

What is the chance the child will have polydactyl?

Answer 29

Dd has the disease so a 100 % chance of the child having polydactyl.