x-linked traits & recombination

Question 1

How many genes are there in humans?

Answer 1

around 20,000

Question 2

How many pairs of chromosomes are there in humans?

Answer 2

23 pairs
-1000 linked genes per chromosomes

Question 3

How are these linked genes inherited? and what happens to Mendel’s second law then?

Answer 3

Linked genes show biases toward parental genotypes and Mendel’s second law gets broken down about independent assortment once genes are inherited together

Question 4

How can we determine the order and location of genes
within a chromosome?

Answer 4

By using recombination frequencies

Question 5

How does recombination occur for linked genes?

Answer 5

Crossing over during meiosis explains recombination

Question 6

recombination can’t get higher than what percentage?

Answer 6

50%

Question 7

Why is there a bias toward parental phenotypes?

Answer 7

Fewer recombinants mean the 2 genes must be linked (on the same chromosome) (violates Mendel’s 2nd Law (independent assortment))

Question 8

how many pairs of autosomes do we have?

Answer 8

22 pairs

Question 9

what is homogametic?

Answer 9

two sex chromosomes that are the same

Question 10

what is heterogametic in humans?

Answer 10

males

Question 11

what is heterogametic?

Answer 11

two different sex chromosomes

Question 12

what is hemizygous?

Answer 12

can only have one x-chromosome

Question 13

inheritance between males and females…

Answer 13

always differs

Question 14

how to find out the genotype by the ratio? (1:1:1:1)

Answer 14

divide by 4 to get the values for all 4 and this is confirmed by Mendel’s second law because they are independently being assorted

Question 15

How are these linked genes inherited? and what happens to Mendel’s second law then?

Answer 15

Linked genes show biases toward parental genotypes and Mendel’s second law gets broken down about independent assortment once genes are inherited together

Question 16

why is there a bias towards parental and not recombination?

Answer 16

those two genes are linked so they are not assorting independently

Question 17

the genes usually stay together but not always why is that?

Answer 17

because of the crossing over during meiosis which forms recombinants

Question 18

what do recombination and crossing over depend on?

Answer 18

Recombination depends on the crossing over and crossing over depends on how close the genes are

Question 19

what is the recombination frequency?

Answer 19

the proportion of recombinant gametes is termed the recombination frequency

Question 20

what is happening during crossing over?

Answer 20

two chromatid of a tetrad cross over at random points and swap genetic material = only one chiasma has formed

Question 21

what is a tetrad?

Answer 21

one from each pair

Question 22

what can be used to find our how close or far apart the genes are in a chromosome?

Answer 22

Gene mapping and recombination frequency can be used to find out how close or far apart they are in a chromosome

Question 23

how to calculate recombination frequency?

Answer 23

• adding up the recombinants
• divide by the total of recombinant+parents

Question 24

what does the calculation of the recombination frequency answer tell us?

Answer 24

The final amount will give us % of gametes/sperm contain a chromosome that is formed by chaisma between the two genes

Question 25

what does a small distance between the two genes mean?

Answer 25

smaller the distance between two genes - the
less likely a chiasma will be formed between them

Question 26

how much recombination frequency will distant unlinked genes have?

Answer 26

Distant (unlinked) genes have a recombination frequency
around 50% (half recombinant and half parental types)

Question 27

how much recombination frequency will closed linked genes have?

Answer 27

Close genes have recombination frequencies of 0-50%

Question 28

what is the relationship between distance and
recombination frequency?

Answer 28

there is a near-linear relationship between distance and
recombination frequency