Genetics

Question 1

what is the null hypothesis always for chi-squared?

Answer 1

there is no significant difference between observed and expected results

Question 2

when the chi-squared test is carried out, what is it carried out to compare?

Answer 2

how well observed and expected match results

Question 3

to find out if there is a significant difference between your observed and expected results, what do you need to compare your chi-squared value to?

Answer 3

critical value

Question 4

what is the critical value?

Answer 4

value of chi squared that corresponds to 0.05 probability level that the difference between observed and expected results is DUE TO CHANCE

Question 5

if chi squared value is larger than / equal to critical value then…

Answer 5

• is significant difference
• between observed and expected
• null rejected

Question 6

if chi-squared value smaller than critical value then…

Answer 6

• no sig difference
• between observed and expected
• null NOT rejected

Question 7

male cats with tortoiseshell phenotypes dont occur.

why?

Answer 7

• Y chromsome doesnt carry allele
• cannot be hetero

Question 8

the allele for polydactyly is dominant.

some cat breeders select for polydactyly.

describe how this would affect the frequences of the homozygous genotypes for this gene in their breeding populations over time?

Answer 8

• homo dominant inc
• homo recessive dec

Question 9

in birds, males are XX and females are XY.

use this info to explain why recessive, sex linked characteristics are more common in female birds than male birds?

Answer 9

• females have one allele
• recessive allele always expressed

Question 10

explain the advantage of presenting results as a ratio?

Answer 10

• able compare (valid)
• number / sample size may vary

Question 11

Answer 11

gene/loci on same chromosome

Question 12

how many antigen determining alleles will be present in a white blood cells?

give a reason for your answer?

Answer 12

• 2
• white blood cells = diploid

Question 13

explain 2 reasons why the fruit fly is a useful organism for studying genetic crosses?

Answer 13

• large number of eggs - reduces sampling error
• simple nutrient medium - reduces cost

Question 14

suggest why observed ratios are often not the same as expected ratios?

Answer 14

• fertilisation is random
• population sample small

Question 15

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 15

• males have one allele - only need 1 recessive allele
• females ned 2 recessive alleles

Question 16

in an investigation, the numbers for tongue rolling and thumb characteristics do not add up to 200.

for each characteristic suggest one reason why the numbers do not add up to 200?

Answer 16

• tongue rolling - some people not willing to tell
• thumb - thumb bending subjective

Question 17

Answer 17

• 4 and 3
• both 4 and 3 are carries / hetero

Question 18

explain one piece of evidence from the diagram which proves that the allele for Tay-Sachs disease is not on the X chromosome?

Answer 18

• 11 affected, 3 not
• 3 doesnt have recessive allele on his chromsome

Question 19

suggest why the actual percentage of heterozygotes is likely to be lower in future generations than the answer you would have calc?

Answer 19

affected individuals usually dont reproduce

Question 20

suggest advantages of using island populations?

Answer 20

• can record all individuals on small islands
• less sampling error
• diff rates of mutation
• inbreeding more likely
• little gene flow

Question 21

the geneticist concluded that arm-folding is NOT determined by a single gene with a dominant allele and a recessive allele.

use info from figure 2 to explain why she reached this conclusion?

Answer 21

• if R recessive, R x R parents cant produce L offpsring
• if L recessive, L x L parents cant produce R offspring
• R x R and L x L parents produce both types of offspring

Question 22

Answer 22

both twins folded arms differently

Question 23

Answer 23

• 1,2 and 5
• 1 must pass on recessive allele to 5

Question 24

explain why scientists used the same restriction endonuclease enzyme on each DNA sample?

Answer 24

• cut DNA at same base sequence
• so get fragments with required gene

Question 25

explain why cells in mitosis were used?

Answer 25

• chromosomes visible
• can see which chromosome DNA probe attaches to

Question 26

Answer 26

• 2 is not colour blind and 4 is colour blind
• so 2 must be hetero

Question 27

Answer 27

gene/loci on same chromsome

Question 28

use your knowledge of gene linkage to explain these results?

Answer 28

• GgNn individuals produce mainly GN and gn gametes
• crossing over produces some Gn and gN gametes
• fewer Ggnn and ggNn individuals
• GN linked with gn

Question 29

explain why the number of people showing LP would rapidly increase once selection for this condition had been established?

Answer 29

• domiant allele
• always expressed in phenotype

Question 30

lactase persistence is caused by a mutation in DNA.

this mutation doesnt occur in the gene coding for lactase.

suggest and explain how this mutation causes LP?

Answer 30

• mutation in promoter gene for TF
• lactase gene continues to be transcribed

Question 31

explain evidence that allele for white fur is recessive

Answer 31

parents are hetero

Question 32

evidence from a diagram that muscular dystrophy is

sex linked

Answer 32

only seen in males

Question 33

evidence that Li-Fraumeni syndrome caused by

dominant allele

Answer 33

C doesnt have condition = carrier

Question 34

evidence that Li-Fraumeni syndrome

not sex linked

Answer 34

• father (A) would pass on X chromosome to daughter
• shes not affected

Question 35

the families history of cancer was investigated when a person asked for genetic counselling.

at the time she was 25 years old

what advice could a genetic counsellor give about her prbability of developing cancer?

Answer 35

• dont know if cancer will develop
• dont know if father hetero

Question 36

Li-Fraumeni syndrome is caused by a mutation affecting a tumour suppresor gene called TP53.

the gene codes for protein that initiated death of cells where damaged DNA cannot be repaired.

mutated TP53 gene leads to production of non-functional protein

suggest how non-functional protein may lead to cancer

Answer 36

• mutation changes DNA of cell
• damaged DNA not repaired
• mutation leads to loss of control of cell division
• cells carried to other parts of body