genetics and inheritance

Question 1

Whats meant by codominant alleles

Answer 1

*both alleles are equally dominant
*in phenotyope expressed

Question 2

A breeder had expected equal numbers pf chocolate and cinnamon kittens from the cross between choc males and blk females. Explain why the acc number were diff than expected

Answer 2

*offspring ratios not fixed
*gametes may not be produced in equal numbers
*small sample

Question 3

Male fruit flies are more likely than female fruit flies to show a phenotype produced by a recessive allele carried on the X chromosome explain why

Answer 3

*males have one allele
*females have 2 recessive alleles

Question 4

What is meant by the term genotype?

Answer 4

Genetic constitution of an organism

Question 5

What is meant by the term phenotype?

Answer 5

The expression of genetic constitution
and its interaction with the environment

Question 6

What are alleles and how do they arise?

Answer 6

Variations of a particular gene (same locus) → arise by mutation (changes in DNA base sequence)

Question 7

How many alleles of a gene can be found in diploid organisms?

Answer 7

● 2 as diploid organisms have 2 sets of chromosomes (chromosomes are found in homologous pairs)
○ But there may be many (more than 2) alleles of a single gene in a population

Question 8

Whats a sex linked gene

Answer 8

A gene located on a sex chromosome normally the X chromosome

Question 9

What is epistasis?

Answer 9

Interaction of (products of) non-linked genes where one masks / suppresses the expression of the other

Question 10

Explain how autosomal linkage affects inheritance of alleles

Answer 10

● Two genes located on same autosome (non-sex chromosome)
● So alleles on same chromosome inherited together
○ Stay together during independent segregation of homologous chromosomes during meiosis
● But crossing over between homologous chromosomes can create new combinations of alleles
○ If the genes are closer together on an autosome, they are less likely to be split by crossing over

Question 11

Whats autosomal linkage

Answer 11

● Two genes located on same autosome (non-sex chromosome)

Question 12

Suggest why in genetic crosses, the observed phenotypic ratios obtained in
the offspring are often not the same as the expected ratios

Answer 12

● Fusion / fertilisation of gametes is random
● Autosomal linkage / epistasis / sex-linkage
● Small sample size → not representative of whole population
● Some genotypes may be lethal (cause death)

Question 13

when can a chi-squared (X2) test be used

Answer 13

● to see if observed results are significantly different from expected results (frequencies)
○ Eg. comparing the goodness of fit of observed phenotypic ratios with expected ratios
● Data is categorical (can be divided into groups eg. phenotypes)

Question 14

Describe how a chi-squared value can be analysed

Answer 14

1. Number of degrees of freedom = number of categories - 1 (eg. 4 phenotypes = 3 degrees of freedom)
2. Determine critical value at p = 0.05 (5% probability) from a table
3. If X2 value is [greater / less] than critical value at p < 0.05
   ○ Difference [is / is not] significant so [reject / accept] null hypothesis
   ○ So there is [less / more] than 5% probability that difference is due to chance