7.1 Inheritance

Question 1

What does homozygous mean?

Answer 1

having identical pairs of genes for any given pair of hereditary characteristics

Question 2

What does heterozygous mean?

Answer 2

two different alleles for a hereditary characteristic

Question 3

What is a phenotype?

Answer 3

visible characteristics.
the expression of an organisms genetic constitution, combined with its interaction with the environment

Question 4

What is a genotype?

Answer 4

genetic makeup of a person

Question 5

What is an allele?

Answer 5

different versions of a single gene found at the same locus on a chromosome. A single gene could have many alleles

Question 6

Who is the father of modern genetics?

Answer 6

Gregor Mendel

Question 7

What is cystic fibrosis?

Answer 7

a disease that causes thick and sticky mucus to coat the lungs, gut and pancreas. Its caused by recessive alleles FfxFf

Question 8

What is Huntingdon’s disease?

Answer 8

a disease of the nervous system that causes shaking and eventually dementia. Its caused by a dominant allele Cc x cc

Question 9

What is sickle cell anaemia?

Answer 9

a disease that alters the shape of red blood cells, thereby reducing their oxygen capacity, causing weakness and anaemia. Its caused by recessive alleles

Question 10

What are genes and alleles?

Answer 10

• genes control the characteristics of an organism
• often genes have 2 different forms called alleles. For example if a gene controls the colour of a flower, the allele will control the exact colour
• In a pair, one allele may be dominant and another recessive
• Some genetic disorders are caused by recessive genes, others by dominant genes

Question 11

What is a monohybrid cross?

Answer 11

• how a single character is passed on from one generation to another
• allow the genotype of offspring to be predicted.

Question 12

What is a dihybrid cross?

Answer 12

where we consider the inheritance of 2 characteristics at the same time

Question 13

What ratio does a monohybrid cross between 2 heterozygous produce?

Answer 13

3:1

Question 14

What is independent assortment?

Answer 14

• The law of independent assortment means that genes separate independently of each other when gametes are made.
• it means that every possible combination of alleles for every gene is equally likely to happen. This means genes do not influence each other with regard to the sorting of alleles into gametes.

Question 15

What is codominance?

Answer 15

• Codominance is where both alleles for the same characteristic are simultaneously expressed in the heterozygote.
• Neither of the alleles are recessive.
• it influences the phenotypic ratios of monohybrid and dihybrid crosses.

Question 16

What does codominance change the phenotypic ration to?

Answer 16

1:2:1

Question 17

What is autosomal linkage?

Answer 17

• Where two or more genes are located on the same chromosome that are close to one another are likely to be inherited together.
• Linkage shows that some allele combinations are not inherited independently of each other.
• Only 1 homologous pair is needed for all 4 alleles to be present. For genes that aren’t linked, 2 homologous pairs are needed

Question 18

What is recombination?

Answer 18

• When gametes are produced by meiosis, multiple sections of homologous chromosomes are exchanged in a process called recombination.
• If two genes are located in close proximity on the same chromosome, they are more likely to be exchanged together and not separated in recombination.
• The genes are more likely to be transmitted to a gamete together.

Question 19

What are autosomes?

Answer 19

• Autosomes are all the chromosomes except the sex chromosomes (X and Y).
• They are arranged in pairs called homologous chromosomes (one from the father and one from the mother).
• Homologous chromosomes consist of the same genes in the same order along the chromosome.
• There is some variation if the chromosomes have different alleles but the genes are the same.

Question 20

What are sex chromosomes?

Answer 20

In many organisms, the sex chromosomes (X and Y) determine the sex of an individual.
Sex chromosomes differ from autosomes because they are non-homologous.
Non-homologous chromosomes do not consist of the same genes in the same order along the chromosome.

Question 21

What is Hemizygosity?

Answer 21

Hemizygosity means that there is no role of dominance and recessiveness.

Question 22

What are the features of haemophilia?

Answer 22

• X-linked blood disorder
• males are affected if they inherit one copy of the recessive allele
• females can be carriers if they are heterozygous
• females are only affected if they inherit 2 copies of the recessive allele

Question 23

What are homologous chromosomes?

Answer 23

• Chromosomes in diploid organisms exist in homologous pairs.
• Homologous chromosomes consist of the same genes in the same order.
• The only variation between homologous chromosomes is in the alleles.
• Two alleles can be present for one gene.

Question 24

What are multiple alleles?

Answer 24

• only variation between homologous chromosomes is in the alleles
• Homologous chromosomes are made of same genes in the same order
• There may be multiple alleles for a gene at the population level
• multiple alleles have a dominance hierachy

Question 25

What is the function of epistasis?

Answer 25

- Where 2 non-linked genes interact, with one gene either masking or suppressing the other gene - The alleles that are being masked are hypostatic to the epistatic alleles. - Epistasis often involves a pathway where expression of one gene is dependent on the function of another gene.

Question 26

What is recessive epistasis?

Answer 26

- Recessive epistasis is where the epistatic allele (the allele that masks another gene) is recessive. - This means two copies of the epistatic allele must be present for expression of the hypostatic allele to be affected. - In other words where two homozygous recessive alleles mask expression of another allele

Question 27

What is dominant epistasis?

Answer 27

- Dominant epistasis is where the epistatic allele is dominant. - This means only one copy of the epistatic allele must be present for expression of the hypostatic allele to be affected. - In other words where one dominant allele masks expression of multiple other alleles

Question 28

What is Chi-squared?

Answer 28

- Genetic diagrams are used to predict the expected phenotypic ratio of offspring. - Predictions are rarely 100% accurate because of the random nature of gametes fusing during fertilisation. - Chi-squared is used to compare observed phenotypic ratios with expected ratios. - Chi-squared tells us if the difference between the observed and expected ratios are due to chance.

Question 29

When is chi-squared used?

Answer 29

- when variation is discrete not continuous. This means the data are in categories (e.g. Aa and aa). - when data show absolute numbers (whole numbers), normally frequencies. - large sample size - only raw count data allowed - no data values equal zero

Question 30

What is the null hypothesis?

Answer 30

- 'There is no significant difference between observed and expected data, the difference is due to chance'. - The chi-squared test is used to reject or accept the null hypothesis.

Question 31

What is the equation for chi-squared?

Answer 31

X = Σ (O - E)^2/E O = observed values. E = expected values.

Question 32

When do you accept the null hypothesis?

Answer 32

- If the chi-squared value is lower than the critical value so not a significant difference - The difference between observed and expected data is due to chance

Question 33

When do you reject the null hypothesis?

Answer 33

- If the chi-squared value is greater than the critical value so a significant difference - The difference between observed and expected data is NOT due to chance.

Question 34

How many alleles per gene do diploid organisms carry?

Answer 34

2

Question 35

What is a dominant allele?

Answer 35

an allele whose characteristic will always appear in the phenotype, whether one or two are present

Question 36

What is meant by a recessive allele?

Answer 36

an allele whose characteristic only appears in the phenotype if no dominant allele is present, meaning two must be pressent

Question 37

What is meant by codominant alleles?

Answer 37

two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together

Question 38

Define monohybrid inheritance.

Answer 38

where one phenotypic characteristic is controlled by a single gene

Question 39

Define dihybrid inheritance

Answer 39

where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time

Question 40

What is meant by sex-linkage?

Answer 40

where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual

Question 41

Why are males more likely to express a recessive sex-linked allele?

Answer 41

most sex-linked alleles are located on the X chromosome. Therefore males only get one copy of the allele, so will express this characteristic even if its recessive. Since females get two alleles, this is less likely

Question 42

Which parent do males inherit sex-linked characteristics from?

Answer 42

Their mother, since the Y chromosome can only come from their father. Therefore if the mother is heterozygous for sex-linked alleles, she is a carrier and may pass on the trait