autosomal linkage

Question 1

the bigger the sample, the ……

Answer 1

closer the numbers will be to the expected ratio

Question 2

what is autosomal linkage

Answer 2

when two or more genes are located on the same autosome

Question 3

what are autosomes

Answer 3

chromosomes which are not concerned with sex determination (all other pairs of chromosomes, not X or Y)

Question 4

how are autosomes different to sex chromosomes?

Answer 4

• entirely homologous
• each chromosome in the pair codes for the same genes so there are always 2 copies of the gene

Question 5

what are linked genes

Answer 5

genes located on the same chromosome

Question 6

chromosomes and chromatids are … so gametes with …. … ….. form with … … of each allele combination

Answer 6

independently assorted
each possible combination
equal proportions

Question 7

what happens to linked genes in meiosis

Answer 7

• crossing over can result in formation of recombinant chromatids from innermost chromatids
• allele combinations on outermost chromatids do not change

Question 8

why is the proportion of recombinant chromatids smaller than non recombinant

Answer 8

because crossing over is random

Question 9

when chromatids are separated in ……… the allele combinations on the ….. sister chromatids will be passed onto many ……..

some gametes will inherit a …… chromatid

this results in smaller numbers of …… …… than ……

Answer 9

anaphase 2
unchanged
gametes
recombinant
recombinant gametes
non recombinant

Question 10

genes that are found on separate ….. are ……

Answer 10

chromosomes
unlinked

Question 11

unlinked genes undergo …… assortment during meiosis. this results in …… proportions of recombinant and …….. gametes.

Answer 11

independent
equal
non recombinant

Question 12

genes that are found on the ….. autosome are said to be autosomally …..

Answer 12

same
linked

Question 13

the alleles of linked genes stay together during independent assortment unless …….. ……. occurs
crossing over is ……

Answer 13

crossing over
random

Question 14

this means that if genes are linked there are likely to be higher proportions of gametes with the ….. allele combinations as the parent cell and fewer ….

Answer 14

same
recombinants

Question 15

the closer together the two genes are on the chromosome the …. crossing over is likely to occur. this is called …. linkage.

Answer 15

less
tight

Question 16

the effect of autosomal linkage on offspring phenotypic ratios depends on:

Answer 16

• genotypes of 2 parents
• arrangement of alleles on parent chromosomes
• distance between linked genes

Question 17

what happens when two genes are located on the same chromosome?

Answer 17

the alleles for each gene linked on the same chromosome will be inherited together - impacts predicted gametes

Question 18

if allele Y and R are linked, and allele y and r are linked, what would the gametes be?

Answer 18

either RY or ry (they are linked on the same chromosome)

Question 19

why would the observed ratio of autosomal linkage be different to the expected ratio?

Answer 19

crossing over must have occured during meiosis to make new combinations of gametes

Question 20

explain why there are more Y&R peas and G&W peas than G&R and Y&W peas

Answer 20

1. yellow and round (RRYY) and green and wrinkled (rryy) are most common phenotypes - they are result of gametes RY+RY and ry+ry fusing
2. these are most common as they are not formed by crossing over
3. fewer g&w due to being recessive
4. crossing over is rare - not many Ry or rY gametes will be made
5. not many genotypes RRyy or rrYY will form
6. suggests why not many Y&W or G&R peas formed