B1 More Genetic Diagrams

Question 1

What are gametes in sexual reproduction?

Answer 1

Reproductive cells from the mother and father (egg and sperm)

Question 2

What is contained in a each gamete?

Answer 2

One copy of each chromosome, so gametes only have one version of each gene, one allele.

Question 3

How are offspring produced? (We’re thinking about the gametes)

Answer 3

The chromosomes from a male gamete get mixed up with those from a female gamete.

Question 4

What does the offspring end up with?

Answer 4

Pairs of chromosomes and two alleles for each gene.

Question 5

What does it mean if the alleles are different?

Answer 5

The organism has instruction for two different versions of a characteristic but it only shows now version.

Question 6

What is the version of the characteristics displayed decided by?

Answer 6

The dominant allele

Question 7

What is the name for the allele that is not displayed when an organism has different alleles?

Answer 7

Recessive allele

Question 8

If a characteristic is caused by a recessive allele, when is it displayed?

Answer 8

When both alleles are recessive.

Question 9

How are dominant alleles shown in genetic diagram?

Answer 9

As a capital letter

Question 10

How are recessive alleles shown in a genetic diagram?

Answer 10

With a small letter

Question 11

What does it mean if you are homozygous for a trait?

Answer 11

You have alleles the same for that particular gene.

Question 12

What does it mean if you are heterozygous for a trait?

Answer 12

You have two different alleles

Question 13

What is it called if you have two alleles the same?

Answer 13

Homozygous

Question 14

What is it called if you have two alleles that are different?

Answer 14

Heterozygous

Question 15

What is a genotype?

Answer 15

The alleles an organism has.

Question 16

What is a phenotype?

Answer 16

The characteristics an organism displays.

Question 17

What is single gene inheritance?

Answer 17

A characteristics controlled by a single gene, e.g. Blood group

Question 18

What can genetic diagrams help predict?

Answer 18

The phenotype of the offspring, when you know the genotype of the parents.

Question 19

Look at genetic diagrams and practice drawing them

Answer 19

P7 in the revision guide.

Question 20

The height of garden pea plants is controlled by a single gen with two alleles. The allele for tall plants (T) is dominant over the allele for dwarf plants (t). Two heterozygous pea plants are crossed. Draw a genetic diagram to find what proportion of the offspring would be expected to be dwarf plants (3 marks)

Answer 20

I in 4, need to see a diagram

Question 21

How many chromosomes are there in every human body cell?

Answer 21

23 pairs

Question 22

How are the 23rd pair of chromosomes in the human body cell labelled?

Answer 22

XY or XX

Question 23

What do the sex chromosomes decide?

Answer 23

Whether you are male or female

Question 24

What type of chromosomes are XX or XY?

Answer 24

Sex chromosomes

Question 25

What are male sex chromosomes labelled?

Answer 25

XY

Question 26

What are female sex chromosomes labelled?

Answer 26

XX

Question 27

How is sex determined?

Answer 27

By genes

Question 28

What does Y chromosome carry?

Answer 28

A gene which makes an embryo develop into a male as it grows, by stimulating growth of the testes

Question 29

Draw a genetic diagram for sex inheritance

Answer 29

XX. (Female parent) X. X. X. XX. XX. (Male parent) XY Y. XY. XY

Question 30

What do a sex inheritance genetic diagram show?

Answer 30

Two XX genotypes, two XY genotypes There is a 50% chance of having a boy or girl Ratio 50:50 boys to girls

Question 31

What is CF (cystic fibrosis)?

Answer 31

A genetic disorder of the cell membrane

Question 32

What is CF (cystic fibrosis) caused by?

Answer 32

A recessive allele, which is carried by about 1 in 30 people

Question 33

People with only one copy of the recessive gene for cystic fibrosis are called what?

Answer 33

Carriers

Question 34

How does having one copy of the recessive gene affect a person?

Answer 34

Because the allele is recessive they won’t have the disorder, they are known as carriers.

Question 35

If a child has a chance of inheriting the disorder cystic fibrosis, what must be true?

Answer 35

Both parents either have the disorder themselves or are carriers.

Question 36

Draw a family tree genetic diagram to show the likelihood of a child having cystic fibrosis if both parents are carriers. Ff carrier FF unaffected ff has CF

Answer 36

1in 4 chance see p8 for diagram (25%) 1 in 2 chance of being a carrier (50%)