3.4

Question 1

What did Mendel discover and how?

Answer 1

Mendel discovered the principles of inheritance with experiments in which large number of pea plants were used

He used pea plants because they can be artificially cross-pollinated, breed quickly, and show many clear phenotypes

He collected lots of quantitative results:
- this is significant because he had lots of replications (pioneer in reliability)
- repeats can be compared with each other
- statistical tests can be done

He concluded that there were hereditary factors (genes) showing dominant or recessive properties and that hereditary factors don’t blend but remain unchanged from one generation to the next

Question 2

Gamete Production

Answer 2

• gametes are produced by meiosis where the number of chromosomes is halved—> gametes are haploid cells
• Haploid cells contains one chromosome of each homologous pair and therefore only one alleles of each gene

Question 3

Define homozygous

Answer 3

having 2 identical alleles of a gene

shown as AA, aa

Question 4

define heterozygous

Answer 4

having 2 different alleles of a gene

shown by Aa

Question 5

define dominant

Answer 5

an alleles which is expressed in the phenotype even if only one copy of the allele is present

shown by capitalisation A

Question 6

define recessive

Answer 6

an allele which is only expressed in the phenotype of two copies of the allele is present

shown by small letter aa

Question 7

define genotype

Answer 7

all the allele that a cell/organism has

Question 8

define phenotype

Answer 8

the outward expression of a cells/organisms genotype

Question 9

Construction of punnet grids for predicting outcomes of monohybrid crosses

Answer 9

1. parental phenotype
2. parental genotype
3. gametes
4. punnet grid
5. offspring genotypes (f1)
6. offspring phenotype (f1)

Question 10

What is the general pattern for the ratio of offspring phenotypes from a monohybrid cross between 2 heterozygotes?

Answer 10

3:1

Question 11

What happens if an organism shows recessive characteristics in its phenotype?

Answer 11

it must have homozygous recessive genotype (eg bb)

Question 12

What happens if an organism shows a dominant characteristic in its phenotype?

Answer 12

it may either have a heterozygous genotype (eg Bb) or have a homozygous dominant genotype (eg BB)

Question 13

Explain what is meant by co-dominance? And what is the general pattern for the ratio of offspring phenotypes from a monohybrid cross between 2 heterozygotes when alleles are codominant?

Answer 13

2 alleles which are equally expressed in the phenotype

1:2:1

2 is the codominant phenotypes

Question 14

Comparison of predicted and actual outcomes of genetic crosses using real data

Answer 14

Question 15

Why do actual outcomes of genetic crosses not always correspond to predicted ratios?

Answer 15

because each time an offspring is born, it is independent of the previous one. the predicted outcomes are just based on portability’s

Question 16

Inheritance of ABO blood groups

Answer 16

• the gene for blood group has three alleles: I^A, I^B, and i
• I^A and I^B are codominant alleles
• both are dominant over i which is recessive

Question 17

Blood transfusions

Answer 17

Question 18

What is cystic fibrosis? show how two individuals who don’t suffer from CF may have a child sufferer

Answer 18

• cystic fibrosis is an autosomal recessive disorder caused by a mutation of the CFTR gene on chromosome 7
• it causes unusually thick and sticky mucus to be produced in lungs which leads to chest infections, shortness of breath, coughing, and may even cause intestinal blockages

Question 19

What is Huntington disease? and using a genetic diagram show the probability of a person who has huntingtons disease passing it on to a child

Answer 19

• huntingtons is an autosomal dominant disorder caused by a mutation of the HTT gene on chromosome 4, which causes neural degeneration
• symptoms include:
  difficulty focusing, memory
  lapses, depression, clumsiness, muscle spasms

Question 20

Sickle cell anemia

Answer 20

sickle cell anemia is an autosomal co-dominant disorder

Question 21

What is meant by the term sex-linkage?

Answer 21

sex linked genes are located on either of the sex chromosomes, X or Y

Question 22

If a recessive condition is caused by a gene on the X chromosome, then which sex is most likely to be affected and why?

Answer 22

males, because they have one copy of X chromosome they have nothing to mask the effects of a recessive allele so they only need one copy to be affected

Question 23

Red-green colour blindness

Answer 23

Red green colourblindness is a sex linked recessive condition, where males cannot be carriers

Question 24

Haemophilia

Answer 24

it’s a genetic disorder where blood doesn’t clot properly

it’s a sex linked recessive disorder where makes cannot be carriers because even if they have one of the recessive alleles that leads to haemophilia (X^h Y) they will have haemophilia as a carrier needs one dominant and one recessive allele

Question 25

Pedigree charts

Answer 25

if male and females are equally affected it is autosomal of not then sex linked

if a disorder/condition doesn’t appear every generation it is recessive if it does then dominant

if a sufferer is born to two unaffected parents it is recessive. if a sufferer is born to a sufferer it is dominant

if there are no unaffected carriers then it is dominant

Question 26

How are new alleles formed?

Answer 26

formed from other alleles by mutations

Question 27

What are consequences of gene mutations?

Answer 27

• can cause uncontrolled cell division (tumours and cancer)
• can cause diseases

Question 28

What happens if mutations occur in body cells? or gamete producing cell?

Answer 28

body cells:
mutations eliminated when the cell/organism dies or

gamete:
can be passed into offspring
origin of genetic diseases

Question 29

briefly describe 2 nuclear incident that have taken place in the last 100 years

Answer 29

The bombing of hiroshima and nagasaki- detonated atomic bombs in WWII in 1945

The Chernobyl accident- explosion of nuclear reactor core in Ukraine 1986

Question 30

What were some long term consequences of radiation exposure?

Answer 30

-increased risk of cancer formation (tumour)
- increased mutations (still births, malformation, death)
-

Question 31

What was released into the atmosphere following the Chernobyl accident? and what we’re the effects on human health

Answer 31

• radioactive isotopes with much longer half lives were released into atmosphere (iodine, uranium, xenon)
• thyroid disease/cancer cases increased significantly due to radioactive iodine
• increased congenital abnormalities