Phenotypic ratios

Question 1

What is linkage and how can it affect offspring?

Answer 1

linkage- meaning the genes are located on the same chromosome

can cause observed ratios to be sig different from expected

Question 2

What is autosomal linkage?
How does it affect inheritance?

Answer 2

both genes are found on the same chromosome
if they are closer together, less likely crossing over will occur= inherited as one unit

found on autosomes- non-sex chromosomes

Question 3

How are linked genes inherited?

Answer 3

inherited as one unit

during meiosis…
genes close together = less likely crossing over will happen= behave more like monogenetic inheritance
when they are further apart= crossing over more likely= lots of different combinations= recombinant offspring

Question 4

What are recombinant offspring?

Answer 4

offspring that have diff combinations of alleles than either parent

can result from linked genes

the closer the genes are on the chromosome, the less likely they are to be separated during crossing over and the fewer recombinant offspring produced

Question 5

What is recombination frequency?
how to you calculate this?

Answer 5

measure of the amount of crossing over that has happened in meiosis

= number of recombinant offspring/total number of offspring

recombination frequency of 50% =no linkage and the genes are on sep chromosomes
less than 50%= is gene linkage and the random process of independent assortment has been hindered

degree of crossing over= determined by how close the genes are on the chromosome
closer= less likely to be sep during crossing over

Question 6

What are 2 reasons that an expected genotypic/phenotypic ratio may be different to an expected one?

Answer 6

autosomal linkage

epistasis

Question 7

What is epistasis?

Answer 7

interaction of genes at different loci

gene regulation is an example - regulatory genes control the activity of structural genes- EG. lac operon

EG. one gene could code for a protein , causing another gene to not be expressed

Question 8

What are the 2 types of epistasis?

Answer 8

dominant epistasis
if a homozygous or heterozygous dominant combination caused the effect

recessive epistasis
homozygous recessive combination causes the effect