CELS 191 Lecture 20 Flashcards
(22 cards)
are X and Y chromosomes homologous
no
does sex determination vary within the animal kingdom
yes
why are males more likely to have X linked traits
because they only have one X chromosome. if females inherit the trait on only one of their chromosomes they don’t express the trait
what are the chances that a father who has an x linked trait will pass it on to his daughters
100%
what are the chances that a father with an X linked trait will pass it on to his sons
0%
if a mother is a dominant homozygote for an x linked trait what are the chances that she will pass on the trait to her daughters
the daughters will have the normal phenotype but will be carriers of the mutation
if a carrier of an x linked trait (female) mates with a normal male what are the chances that her offspring will inherit the trait
50% for male and female offspring - daughters will only be carriers and sons will exhibit the trait
can males be carriers of x linked traits
no
if a carrier of an x linked trait mates with a male with the trait what are the chances the offspring will inherit the trait
there is a 50% chance that each child will have the trait. daughters who do not have the trait will still be carriers, whereas males without the trait will be completely free of the allele
how many genes are there in humans
around 20,000
how many chromosomes are there in humans
23 pairs
what are linked genes
genes located close together on the chromosome that are therefore more likely to be inherited together
how are linked genes inherited
linked genes show biases towards parental phenotypes
how can we determine the order and location of genes within a chromosome
using recombination frequencies
if two individuals mate and the offspring genotypes lean more towards the parental types than expected from expected frequencies what does this suggest
that the two genes do not sort independently - they are linked on the same chromosome
what is recombination frequency
the proportion of recombinant gametes
what causes recombinant gametes
crossing over
how do you calculate the recombinant frequency of a cross
add together the number of offspring that occurred as a result of recombination and divide it by the total number of offspring included in the cross
the smaller the distance between two genes the ____ likely a chiasma will be formed between them
less
distant (unlinked) genes have recombination frequencies around ___
50% - half recombinant and half parental types
close (linked) genes have recombination frequencies of ____
0-50%
what is the relationship between distance and recombination frequencies
near linear
