extra questions b12

Question 1

What is a dominant allele?

Answer 1

An allele that is always expressed

Question 2

Person 1 is heterozygous.
Explain how above figure shows that person 1 is heterozygous.

Answer 2

• person 1 has polydactyly so must have D
• person 5 who does not have polydactyly so must have d from person 1

Question 3

The woman continues to have injections of FSH.
The woman has a child with a man who is heterozygous for the FSH gene.
Explain why the probability that the child will be able to produce FSH is 0.5.

Answer 3

• mother has hh so passes on h
• father has Hh so passes H or h with equal probability
• so child will be Hh with 0.5 probability and produces FSH

Question 4

Explain why the change in the number of chromosomes in meiosis is important.

Answer 4

• meiosis forms gametes
• two gametes fuse
• so chromosome number is kept constant

Question 5

Meiosis produces cells that are genetically different.
Describe how meiosis produces cells that are genetically different.

Answer 5

• random chromosome from each pair (of chromosomes)
• moves to one end of the cell

Question 6

Describe where DNA is found

Answer 6

In chromosomes, in nucleus

Question 7

Describe how embryos can be screened for the alleles that cause genetic disorders

Answer 7

DNA isolated from embryo
probe mixed with embryo DNA
probe (then) binds with embryo DNA
(UV light) to show alleles / gene for disorder

Question 8

The man’s mother also has polydactyly but his father does not

The man is heterozygous for polydactyly.
Explain how the information given above shows that the man is heterozygous for polydactyly.

Answer 8

man has inherited polydactyly allele (from mother)
man has inherited normal recessive allele from father
because father does not have PD allele only has normal allele or father is homozygous recessive

Question 9

What are gametes produced by

Answer 9

meiosis

Question 10

Suggest why it is helpful to take five eggs from the ovary and not just one egg.

Answer 10

greater chance of fertilisation

Question 11

a scientist stated: ‘it is an advantage for people to have the sickle cell anaemia allele in countries where malaria occurs’. evaluate the statement

Answer 11

for:
- people with sickle cell traits do not get malaria
- people with sickle cell traits survive sickle cell anaemia
against:
- people without sickle cell traits can die from malaria
- people with sickle cell anaemia can be severely sick
judgement:
if parents have sickle cell traits then some offspring survive both malaria and sickle cell anaemia

Question 12

suggest one way embryo screening can help people with a family history of a genetic disorder

Answer 12

to inform whether to consider having an abortion

Question 13

a woman has three children. why are they not genetically identical?

Answer 13

• different egg/sperm each time
• each gamete has different DNA

Question 14

explain why a woman might not notice if the embryo doesn’t implant in her uterus

Answer 14

• embryo is very small
• it is lost in menstrual flow

Question 15

Give benefits of understanding the human genome

Answer 15

• Diagnosis of genetic disorders
• research of genetic disorders
• gene therapy or treatment of inherited disorders
• understanding (human) evolution
• tracing human migration patterns
• identification of criminals
• paternity determination

Question 16

Animal 8 is homozygous.
The mutation in animal 7 produced a dominant allele for making low-fat milk.
Give evidence from Figure 2 that animal 7 is heterozygous.

Answer 16

Produces some offspring with high fat milk

Question 17

Why could IVF be used in cows

Answer 17

Takes less time

Question 18

The scientists want to produce a type of cattle that makes large volumes of low-fat milk. The scientists will selectively breed some of the animals shown in Figure 2. Describe how the scientists would do this.

Answer 18

• Find female with low(est) fat in milk and highest milk yield
• find male whose female offspring have high(est) milk yield and lowest fat in milk
• cross the best (for both features) female with the best male
• select best offspring (for both features) from each generation and repeat for several generations

Question 19

The parents shown in the diagram above have five children. Give reasons why these children all look different from each other

Answer 19

• multiple genes determine appearance
• different combinations of alleles
• from different egg/sperm
• different environmental effects

Question 20

The doctors expect half the embryos produced to be female.
Explain why.

Answer 20

50% sperm have X chromosome and 50% sperm have Y chromosome

all eggs have X (chromosome)