Topic 6b- Genetics

Question 1

What are the male chromosomes?

Answer 1

XY

Question 2

What are the female chromosomes?

Answer 2

XX

Question 3

What are the chances that a baby is male / female?

Answer 3

50 / 50

Question 4

How many alleles do normal cells in an organism have?

Answer 4

2

Question 5

How many alleles do gametes have?

Answer 5

1

Question 7

What does homozygous mean?

Answer 7

If an organism has two alleles for a particular gene that are the same

Question 8

What is it called when an organism has two alleles for a particular gene that are the same

Answer 8

Homozygous

Question 9

What does heterozygous mean?

Answer 9

When an organisms two alleles for a particular gene are different

Question 10

What is the allele that is shown called?

Answer 10

The dominant allele

Question 11

What is the allele that doesn’t show up?

Answer 11

recessive

Question 12

What is a genotype?

Answer 12

The combination of alleles that an organism has

Question 13

What is a person’s phenotype?

Answer 13

The physical characteristics that are displayed due to their genotype

Question 14

What is single gene inheritence?

Answer 14

One gene is inherited from the father and one gene is inherited from the mother (it’s just a fance word for basically normal inheritence)

Question 15

What are the two inherited disorders you need to know at GCSE?

Answer 15

cystic fibrosis and polydactyly

Question 16

What is cystic fibrosis?

Answer 16

An inherited disorder of cell membranes resulting in the body producing lots of thick mucus in the air passages and in the pancreas

Question 17

Is the allele that causes cystic fibrosis dominant or recessive?

Answer 17

recessive

Question 18

What are carriers (in reference to genetic disorders e.g. cystic fibrosis)

Answer 18

people with only one copy of the allele (therefore they are heterozygous) meaning that they have no symptoms

Question 19

What is polydactyly?

Answer 19

An inherited disorder where someone’s born with extra fingers or toes

Question 20

Is the allele for polydactyly dominant or recessive?

Answer 20

dominant

Question 21

What is a family tree in genetics?

Answer 21

A diagram that shows how a characteristic (or disorder) is inherited in a group of related people.

Question 22

What is embyronic screening?

Answer 22

A way of detecting disorders such as cystic fibrosis in embryos

Question 23

In what was can embryonic screening be done? How do they work?

Answer 23

• Pre-implantation genetic diagnosis (PGD) - During IVF the cells in an embryo can be removed and analysed, therefore embryos with ‘healthy’ alleles could then be implanted into the mother while the others destroyed.
• Chronic villus sampling (CVS) - Usually carried out between 10-13 weeks of pregnancy CVS involves taking a sample from part of the placenta and analysing their genes (since the placenta develops from the same original cell and therefore genes as the embryo) after analysis the parents can decide whether or not to terminate the pregnancy

Question 24

What are arguments in support of screening?

Answer 24

• It helps stop people from suffering from suffering certain inherited disorders
• Treating disorders costs the government a lot of money so screening could reduce healthcare costs
• During IVF most of the embryos are destroyed anyway so PGD just ensures the one that’s selected is healthy
• If an inherited disorder is diagnosed through CVS, parents don’t have to have a termination- but it does give them a choice

Question 25

What are arguments against screening?

Answer 25

• There could come a point where everyone screens embryos and pick the most ‘desired one’
• It implies that people with genetic disorders are undesirable- this could increase prejudice
• After PGD the rejected embryos are destroyed and some see this as unethical
• There’s a risk that CVS could cause a miscarriage
• Screening embryos is expensive

Question 26

Who was Gregor Mendel?

Answer 26

• Austrian monk
• Trained in mathematics and natural history at the University of Vienna
• Used pea plants to look at how characteristics in plants were passed from one generation to the next

Question 27

What was Mendel’s pea plant experiment?

Answer 27

1. He crossed a tall pea plant and a dwarf pea plant
2. All the offspring were tall pea plants
3. He crossed two of the tall pea plants
4. Resulting in 3 tall pea plants and 1 dwarf pea plant
5. From this Mendel had shown that the height characteristic in pea plants was determined by seperately inherited “hereditary” units passed on from each parent

Question 28

What conclusions did Mendel reach from his experiments on pea plants?

Answer 28

1. Characteristics in plants are determined by “hereditary units”
2. Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent
3. Hereditary units can be dominant or recessive

Question 29

What is the timeline of events starting with Mendel publishing his research that we need to know for GCSE?

Answer 29

(note the dates aren’t that important- more the order)
1866- Mendel publishes work
1884- Mendel’s death
Late 19th century- Scientists became familiar with chromosomes. They were able to observe how they behaved during cell division.
Early 20th century- Scientists realised that there were striking similarities with how chromosomes and Mendel’s ‘units’ acted.
Mid 20th century- scientists discovered the structure of DNA