Topic 6b Genetics

Question 1

How many pairs of chromosomes are found in human cells

Answer 1

23

Question 2

How many of the 23 pairs of human chromosomes determine sex

Answer 2

Only 1 pair of the human chromosomes determine sex. They are labelled XY or XX.

Question 3

To which gender is the XY chromosome associated with

Answer 3

Males have the XY chromosome. The Y chromosome is what causes male characteristics

Question 4

Which pair of chromosomes do females have

Answer 4

Females have two X chromosomes XX. The XX combination is what allows female characteristics to develop

Question 5

True or false all sperm cells carry the Y chromosome

Answer 5

False, there is a 50% chance that the sperm cell will carry either the X chromosome or the Y chromosome. The X and Y Chromosome form the original cell are drawn apart during the first division of Meiosis.

Question 6

What is meiosis

Answer 6

Meiosis is gamete cell division by which one cell divides 4 daughter cells genetically different each with half the number of chromosomes of the parent cell 23

Question 7

What are alleles

Answer 7

Alleles are different versions of the same genes.

For Example the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour

Question 8

What is meant by the term Hetrozygous

Answer 8

Heterozygous means that an organism has two different alleles of a gene. For example, pea plants can have red flowers and either be homozygous dominant (red-red), or heterozygous (red-white).

Question 9

What is meant by the term homozygous

Answer 9

Homozygous means that the organism has two copies of the same allele for a gene. Example A person who has 2 alleles for brown eyes would be considered Homozygous Dominant

Question 10

The allele for a characteristic that is shown in a person i.e. Brown eye colour is known as what

Answer 10

Dominant allele

Question 11

For an organism to show a recessive characteristic what would its alleles look like in terms of letters

Answer 11

Both its alleles would have to be recessive e.g. cc

Question 12

What is a genotype

Answer 12

A genotype refers to the allele combination an organism has for a particular characteristic/trait (usually written as letters) You could have the genotype Bb for hair colour Total Set of genes

Question 13

What is a phenotype

Answer 13

The phenotype is the visible characteristics you have which occur as a result of your genes e.g. blue eyes, blonde hair Physical expression

Phenotype = Physical (physical expression as a result of genes)

Genotype = Genes (Combination of alleles for a particular trait)

Question 14

Give an example of a characteristic controlled by a single gene

Answer 14

Fur colour in animals, Red- Green colour blindness in humans

Question 15

What are inherited disorders

Answer 15

Inherited disorders are disorders caused by a faulty allele and can be passed to an individuals offspring.

Question 16

What sub cellular structures does cystic fibrosis affect

Answer 16

Cell membrane mucus build up in pancreas

It affects the cell membranes resulting in a thick mucus build up in the air passages and the pancreas

Question 17

Is cystic fibrosis caused by the dominant or recessive allele

Answer 17

It is caused by the recessive allele, people with both copies of the recessive allele will have the disease i.e rr

Question 18

What is Polydactly and what allele is it caused by

Answer 18

Polydcactyly is a inherited disorder where a baby is born with extra fingers or toes and it is caused by the dominant allele

Question 19

Why would an embryo be screened before it is inserted into its mothers uterus during IVF

Answer 19

In order to see if the embryo carries any inherited disorders

Question 20

Give the 2 methods used for embryonic screening

Answer 20

Pre Implantation genetic diagnosis and Chronic Villus sampling

PGD and CVS

Question 21

List the Pros and Cons for Embryonic screening

Answer 21

Pros:

• It helps to stop people suffering from disorders
• Treating disorders costs a lot of Money so screening can reduce costs
• Preimplantation Genetic Disorder ensures only healthy embryos are selected

Cons:

• There may come to a point where everyone wants to screen there embryos so they can pick the most desirable one
• It implies people with genetic disorders are undesirable, this could increase prejudice
• After PGD rejected embryos are destroyed which could of become human ;lives
• Screening embryos is expensive

Question 22

If D represents the allele for polydactyly and d represents the allele for an unaffected person, give the possible genotypes of a person with polydactyly

Answer 22

DD, Dd

Question 23

Greg is Homozygous for the polydactyly allele. Which of the following shows Greggs Genotype:

1. DD
2. dd
3. Dd
4. dDd

Answer 23

1. DD

Polydactyly is a Dominant allele disorder