Inheritance - 2

Question 1

What is the expected phenotypic ratio for monohybrid F2 offspring?

Answer 1

3:1

Question 2

What are autosomes?

Answer 2

Chromosomes that do not determine the sex of an organism

Question 3

What is an organisms genotype and phenotype?

Answer 3

Genotype - organisms genetic makeup
Phenotype - organisms displayed characteristics

Question 4

What is the hypostatic gene?

Answer 4

Gene whose expression is blocked or affected by another gene

Question 5

What is the locus of a gene?

Answer 5

Specific position of a gene on a chromosome

Question 6

What are pedigree charts and what are their typical features?

Answer 6

• offer a visual method to track phenotypes and familial relationships over generations
• males represented by squares and females by circles
• lines show relationships between parents and offspring
• shading within a shape indicates presence of a trait

Question 7

What is codominance?

Answer 7

Occurs when two different alleles are equally expressed in an organisms phenotype, so both alleles are present as observable characteristics

Question 8

What is the expected phenotypic ratio for codominance F2 offspring?

Answer 8

1:2:1

Question 9

What are dihybrid crosses and what can they help to show?

Answer 9

• show simultaneous inheritance of two genes controlling separate characteristics
• can help to determine whether genes are linked and calculate expected phenotypic ratios

Question 10

What is the chi-squared test used for?

Answer 10

• statistical tool scientists use to measure differences between observed and expected experimental outcomes

Question 11

What is epistasis?

Answer 11

Interaction between genes where one gene affects or masks the expression of another gene

Question 12

What is recessive epistasis?

Answer 12

• occurs when the epistatic gene must be homozygous recessive to block the expression of the hypostatic gene
• e.g. gene B produces melanin production, and the melanin is required for the colour, so if it is recessive and no melanin is produced, it will block whichever colour gene there is

Question 13

What are sex-linked characteristics and where do they tend to be found?

Answer 13

• genes located on the X or Y chromosomes, meaning that inheritance can be associated with sex
• tend to be located on the X chromosome, due to its larger size

Question 14

What is dominant epistasis?

Answer 14

• occurs when the epistatic gene is dominant and actively modifies or blocks the expression of the hypostatic gene
• e.g. if there is only one dominant gene for the squash to be orange, it will still mask all other colours, no matter what the other alleles are

Question 15

What are the stages of carrying out the chi-squared test?

Answer 15

1) propose an alternative hypothesis - significant difference
2) propose a null hypothesis - assumes there’s no significant difference
3) predict expected phenotypic ratios
4) record observed ratios
5) calculate the chi-squared test
6) compare the result to the critical value - if it’s higher than the value, it suggests the difference is significant

Question 16

What is autosomal linkage and what does this practically mean?

Answer 16

• when genes are located on the same autosome, they are linked
• tend to be inherited together
  Means that:
• there is a non random association of alleles
• phenotypic ratios in dihybrid crosses are different from those expected from independent assortment
• parental allele combinations are persevered over generations

Question 17

What is the expected phenotypic ratio for dihybrid F2 offspring?

Answer 17

9:3:3:1

Question 18

Who are more likely to be affected by sex-linked characteristics?

Answer 18

• males are more likely to be affected by the recessive genes o the X chromosome, as there’s no corresponding allele on the Y chromosome to mask them e.g. haemophilia and colour blindness

Question 19

What is the expected phenotypic ratio for dominant epistatic F2 offspring?

Answer 19

12:3:1

Question 20

What are multiple alleles and what is the most common example?

Answer 20

• Genes that exist in more than two allelic forms, increasing phenotypic diversity
• ABO blood groups are controlled by multiple alleles e.g. Iᴬ, Iᴮ and Iᴼ

Question 21

What is an allele?

Answer 21

Different versions of the same gene that code for variants of the same characteristic

Question 22

What is the expected phenotypic ratio for recessive epistatic F2 offspring?

Answer 22

9:4:3

Question 23

What are the F1 and F2 generation?

Answer 23

F1 - offspring from a cross between individuals with homozygous dominant and homozygous recessive genotypes
F2 - offspring from a cross between two heterozygous F1 individuals

Question 24

What is monohybrid inheritance?

Answer 24

Inheritance where one characteristic is coded for by one gene from each parent

Question 25

What are the two main reasons for deviation from expected phenotypic ratios?

Answer 25

- random fertilisation - gamete fusion is completely random, and small sample sizes could produce skewed results due to chance - linked genes - genes on the same chromosome are usually inherited together, linking certain characteristics together

Question 26

How does crossing over in meiosis affect autosomal linkage?

Answer 26

- potentially separates linked genes - however, when genes are linked, fewer recombinant offspring tend to be produced - probability of linked genes being separated during crossing over is inversely proportional to how close they are on a chromosome