Unit 2 - Genetic Variation

Question 1

What does the overall appearence of an organism depend on?

Answer 1

Its genes (inherited characteristics) and the **effects of the environment **in which it lives.

Question 2

What is a phenotype?

Answer 2

All the observable characteristics of an organism are called its phenotype.

Question 3

What is an organisms genotype?

Answer 3

The full set of genes of an organism

Question 4

What is each different version of a gene called?

Answer 4

An allele

Question 5

What does it mean if an organism is heterozygous?

Answer 5

If the alleles for a characteristic are **different **eg Bb

Question 6

What does it mean if an organism is homozygous?

Answer 6

If alleles for a chatacteristic are the same eg bb/BB

Question 7

What does the characteristics expressed by heterozygous alleles depend on?

Answer 7

Which allele is dominant and which is recessive

Question 8

What is a dominant allele?

Answer 8

Dominant alleles are always expressed in a cells phenotype, only 1 copy of it needs to be inherited for it to be expressed

Question 9

What is a recessive allele?

Answer 9

Recessive alleles are only expressed if **two copies **are inherited

Question 10

What is a test cross used for?

Answer 10

To determine whether an individual is homosygous or heterozygous for a dominant allele

Question 11

What happens during a test cross?

Answer 11

An individual (with an unknown genotype) is crossed with a homozygous recessive individual. The phenotype of the offspring will reveal the unknown genotype.

Question 12

In a test cross, if all the offspring display the dominant phenotype when the parent with the unknown genotype must be..?

Answer 12

**Homozygous **for the characterisitcs

Question 13

In a test cross, if half the offspring show the dominant phenotype, and half show the recessve phenotype, then the parent must be..?

Answer 13

Heterozygous for the characteristic

Question 14

What are sex chromosomes?

Answer 14

Sex chromosomes are either X or Y (xx = girl, xy = boy)

Human cells contain one pair of sex chromosomes which determine the gender of the baby.

Question 15

Why is it the sperm that determines the gender?

Answer 15

Because women can only proudce X gametes

Question 16

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Answer 16

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Question 17

How many bases is DNA made of? and what are they?

Answer 17

4 - A,G,T,C

Question 18

What does each triplet of bases code for?

Answer 18

A particular amino acid

Question 19

What is a monohybrid cross?

Answer 19

What you cross two parents to look at just one characteristic

Question 20

What type of allele does cycstic fibrosis have?

Answer 20

A **recessive **allele

Question 21

What type of allele does Polydactly have?

Answer 21

A dominant allele

Question 22

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Answer 22

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Question 23

List some arguments against embryonic screening

Answer 23

• It may end up with everyone wanting to screen their child and picking a ‘desirable’ child
• The rejected embryo’s are destroyed, when they could have developed into humans
• Implies that disable children are ‘undesirable’ and therefore may cause prejudice
• Screening is expensive

Question 24

List some arguments for embryonic screening

Answer 24

• It will help** stop people from suffering**
• There are **laws that stop it going too far **(parents aren’t allowed to choose the sex, unless its for health reasons)
• During IVF, most of the embryos are **destroyed anyway **- screening just allows the selected ones to be healthy
• Treating diseases costs the government (and taxpayers) money