Inheritance

Question 1

How many pairs of chromosomes do human cells contain?

Answer 1

23 pairs

Question 2

What are the two cells where the chromosomes aren’t in pairs? How many chromosomes do they contain?

Answer 2

• Gametes (female gamete = egg cell, male gamete = sperm cell)
• 23

Question 3

What process are gametes produced by?

Answer 3

Meiosis

Question 4

Where else does this process take place?

Answer 4

In animals and plants

Question 5

What are the plant gametes?

Answer 5

• Pollen ( male)
• Egg cells (female)

Question 6

Do mitosis and meiosis produce genetically identical or non identical cells? Are they sexual or asexual reproduction?

Answer 6

Meiosis- non identical - asexual
Mitosis - identical - sexual

Question 7

What happens in fertilisation? Does fertilisation take place in meiosis or mitosis?

Answer 7

• Fertilisation: The fusion of male and female gametes. Each gamete contains half the number of normal chromosomes. When they fuse the full number (23 pairs) of chromosomes is restored.
• It takes place in meiosis

Question 8

What type of reproduction do we see variation in? Why?

Answer 8

Meiosis
- we see variation because the gametes aren’t genetically identical
- so there is a mixing of genetic information.

Question 9

How many parents are there in asexual reproduction?

Answer 9

1

Question 10

Why are the offspring in asexual reproduction genetically identical? What do scientists call the offspring?

Answer 10

• There is only one parent, so it doesn’t involve gametes.
• Because it doesn’t involve gametes there is no mixing of genetic information.
• Offspring = Clones

Question 11

What happens to the egg cell post fertilisation?

Answer 11

• The fertilised egg cell divides by mitosis, producing an embryo.
• As the embryo develops, the cells differentiate to from different types of cells.

Question 12

Where does meiosis take place? Why isn’t meiosis involved with asexual reproduction?

Answer 12

• In the reproductive organs (testies for males, and ovaries for females.)
• Because asexual reproduction doesn’t involve gametes.

Question 13

Describe the stages of meiosis.

Answer 13

1. Start with a diploid parent cell. This cell has 23 pairs of chromosomes.
2. The chromosomes make identical copies of themselves. There are now 46 pairs of chromosomes.
3. Similar chromosomes pair up and sections of DNA get swapped.
4. The first cell division takes place and the chromosome pairs separate.
5. The second cell division takes place. There are now 4 genetically different gamete cells, each with 23 chromosomes.

Question 14

Describe the stages of mitosis.

Answer 14

1. Mitosis begins with a parent cell containing 23 pairs of chromosomes .
2. The DNA replicates itself to form two copies of each chromosome. The cell now has 46 pairs of chromosomes.
3. The chromosomes line up across the centre of the cell.
4. One set of chromosomes is pulled to each end of the cell and the nucleus divides.
5. The cytoplasm and cell membranes divide to form 2 identical cells. These cells each have 23 pairs of chromosomes.

Question 15

Where is DNA found? Why is DNA our genetic material?

Answer 15

• DNA is found in our chromosomes.
• Scientists call our DNA our ‘genetic material’ because our DNA determines our inherited features.

Question 16

Describe 3 differences between cell division to form sperm cells and cell division to form liver cells.

Answer 16

1. In meiosis there are two divisions, therefore there are 2 divisions to create the sperm cells, whereas in mitosis there is only one division, so there is one division to create the liver cells.
2. There will be 4 sperm cells produced, and they will be genetically different, whereas there will only be two liver cells produced and they will be genetically identical.
3. Each sperm cell will contain 23 chromosomes, whereas each liver cell will contain 46.

Question 17

What does DNA consist of? What is a polymer?

Answer 17

• DNA consists of two strand. Each strand is a polymer.
• Polymers are large molecules that consist of long chains of identical monomers joined together.

Question 18

How is the double helix in DNA formed? Who found the evidence that DNA was shaped like a double helix?

Answer 18

• By the two polymer strands wrapping around each other.
• Rosalind Franklin

Question 19

Does a pair of chromosomes contain the same or different genes?

Answer 19

The same.

Question 20

How are proteins made? What does each gene code for?

Answer 20

• Proteins are made by joining together amino acids.
• Each gene codes for a specific sequence of amino acids to make a specific protein.

Question 21

State 3 benefits to understanding the human genome.

Answer 21

• It helps us to discover our ancestry. We can use the human genome to trace human migration patterns from the past.
• We can search for genes that are linked to a disease. E.g genes that increase the risk of developing cancer.
• It will help us to understand and treat inherited disorders e.g cystic fibrosis.

Question 22

What are alleles?

Answer 22

Alleles are versions of a gene.

Question 23

What are homozygous and heterozygous alleles?

Answer 23

Homozygous = Both alleles are the same eg EE or ee
Heterozygous = Both alleles are different. E.g Ee

Question 24

What is a phenotype?
A recessive allele will show in the phenotype if….

Answer 24

• A phenotype tells us the characteristics caused by a persons alleles.
• A recessive allele will only show in the phenotype if there are two copies present.

Question 25

A dominant allele will show in the phenotype if….

Answer 25

- If there is one copy present.

Question 26

What is a genotype?

Answer 26

The combination of alleles that an organism has for a particular gene.

Question 27

What is cystic fibrosis? How many genes is it controlled by?

Answer 27

- Cystic fibrosis is a disorder of cell membranes. - It is controlled by a single gene.

Question 28

Show the alleles for: 1. A person not carrying cystic fibrosis 2. A person that is a carrier of cystic fibrosis, but not affected by it. 3. A person affected by cystic fibrosis.

Answer 28

1. CC 2. Cc 3. cc

Question 29

In order to have cystic fibrosis what does a person have to inherit?

Answer 29

- They have to have both defective alleles (c). This means they have to inherit the defective allele from both parents.

Question 30

What do we call a person that has one copy of the defective allele for cystic fibrosis?

Answer 30

- We call them a carrier. They do not have cystic fibrosis.

Question 31

1. Draw a punnet square for a father who is not a carrier or affected by cystic fibrosis, and a mother who is a carrier. 2. Calculate the probability their children will: a) not be affected b) be a carrier c) have cystic fibrosis

Answer 31

1. Draw correct punnet square 2. a) 50% b) 50% c) 0%

Question 32

Given that this si just a probability, what could happen?

Answer 32

- More of the children could be carriers, or more of the children may not be carriers.

Question 33

1. Draw a punnet square for a mother and father who are both carriers of cystic fibrosis. 2. Calculate the probability their children will: a) not be a carrier of cystic fibrosis. b) be a carrier of cystic fibrosis c) have cystic fibrosis

Answer 33

1. Draw correct punnet square 2. a) 25% b) 50% c) 25%

Question 34

What sex chromosomes do males have? What about females? What determines your sex?

Answer 34

Males : XY Females : XX One of your pairs of chromosomes.

Question 35

Give one piece of evidence that cystic fibrosis is caused by a recessive allele. (common family tree question)

Answer 35

- If cystic fibrosis was caused by a dominant allele, at least one parent would have to have cystic fibrosis as you only have to have one dominant allele to inherit the disorder.

Question 36

What is polydactyly? What type of allele is it caused by? So will a person with this genotype (Cc) have polydactyly?

Answer 36

- An inherited disorder that causes someone to have extra fingers and toes. - it is caused by a dominant allele - Yes becases they have one dominant allele.

Question 37

Can you be a carrier of the polydactyly allele? Why/ Why not?

Answer 37

- No. - B/c it is caused by a dominant allele, so if you have a dominant allele, you have the characteristic. This is the same for all inherited disorders caused by dominant alleles.

Question 38

Draw a punnet square for a father that has polydactyly (Pp) and a mother that does not have polydactyly (pp). Then calculate the probability that the children: a) Have polydactyly. b) do not have polydactyly

Answer 38

1. Draw correct punnet square. 2. a) 50% of children have polydactyly. b) 50% of children not affected by polydactyly.

Question 39

What is the purpose of embryo screening?

Answer 39

- To test to see if embryos have the alleles for inherited disorders. - Then, the embryos that dint have the defective alleles can be implanted into the woman.

Question 40

Name 3 disadvantages to embryo screening.

Answer 40

- Embryo screening is expensive. Some people think this money should be invested elsewhere in the health service. - Only a small number of embryos are implanted into the woman, but lots are created. This means some are destroyed, which some people think is unethical. - In the future, we may be able to screen embryos to produce offspring with desirable features e.g tallness. Some people find this unethical.

Question 41

Name 2 advantages of embryo screening.

Answer 41

1. You can find out whether the embryo has an inherited disorder. 2. You can decide whether or not to continue with the pregnancy.

Question 42

What is gene therapy?

Answer 42

Gene therapy is the idea that in the future, scientists may be able to correct faulty alleles and treat inherited disorders.

Question 43

What is the definition of a gene?

Answer 43

A small section of DNA on a chromosome.

Question 44

What is the definition of a genome?

Answer 44

The entire genetic material of an organism.