Topic 7A - Genetics DVY *

Question 1

what is a gene?

Answer 1

a sequence of bases on a DNA molecule that codes for a protein which results in a characteristic

Question 2

what is an allele?

Answer 2

a different version of a gene. most plants and animals carry 2 alleles of each gene. the order of bases in each allele so they code for different versions of the same characteristic

Question 3

what is a genotype?

Answer 3

the genetic constitution of an organism - the alleles an organism has

Question 4

what is a phenotype?

Answer 4

the characteristics of the genotype that are expressed, and its interaction with the environment

Question 5

what is dominant?

Answer 5

an allele who’s characteristics always appear in the phenotype. even if there’s only 1 copy

Question 6

what is recessive?

Answer 6

an allele whose characteristics only appear in the phonotype if it is homozygous

Question 7

what is codominant?

Answer 7

alleles that are both expressed in the phenotype - neither are recessive

Question 8

what is the locus?

Answer 8

the fixed position of a gene on a chromosome. alleles of a gene are found at the same locus on each chromosome in a pair

Question 9

what is a homozygote?

Answer 9

an organism that carries 2 copies of the same allele

Question 10

what is a heterozygote?

Answer 10

an organism that carries 2 different alleles

Question 11

what is a carrier?

Answer 11

a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring

Question 12

what is monohybrid inheritance?

Answer 12

the inheritance of a characteristic controlled by a single gene
e.g. N - normal wings
n- small wings

Question 13

what is sickle cell anaemia?

Answer 13

SS - homozygous for sickle cell - red blood cells are misshapen so they don’t carry oxygen properly
NN - homozygous for normal haemoglobin - don’t have disease
SN - in between, patients can still survive but the haemoglobin is a strange shape - but mosquitos can’t pass on malaria

Question 14

what is a dihybrid cross?

Answer 14

when the parents have 2 different genes you can work out the chances of offspring inheriting certain combinations of alleles.
e.g. genotype: RrYy
gametes: RY, Ry, rY, ry
these would go on the top of the punnet square and the other parents can go on the side

Question 15

what is the phenotypic ratio?

Answer 15

the ratio of different phenotypes in offspring
if both parents are heterozygous:
monohybrid - 3:1
dihybrid - 9:3:3:1
codominant - 1:2:1

Question 16

when is a characteristic sex-linked?

Answer 16

when the allele that codes for it is located on a sex chromosome

Question 17

what are most sex linked genes carried on?

Answer 17

the Y chromosome is smaller than the X and carries fewer genes. so most genes are only carried on the X chromosome. (X-linked genes)

Question 18

why are men more likely to express recessive phenotypes for sex-linked genes?

Answer 18

males only have 1 X chromosome, so only have 1 allele for X-linked genes.
so they express the characteristic of this allele even if it’s recessive

Question 19

what are examples of genetic disorders caused by faulty alleles on sex chromosomes?

Answer 19

colour blindness
haemophilia
the faulty alleles are carried on the X-chromosome, so are more common in men than women

Question 20

what is an autosome?

Answer 20

any chromosome that isn’t a sex chromosome

Question 21

what are autosomal genes?

Answer 21

genes located on the autosomes

Question 22

what is autosomal linkage?

Answer 22

genes on the same autosome are said to be linked, they stay together during independent segregation of chromosomes in meiosis I, and their alleles will be passed on to the offspring together.
this only doesn’t happen if crossing over splits them up

Question 23

how can autosomal linkage be identified?

Answer 23

you don’t get the phonotypic ratio you expect in the offspring.
the linked alleles are inherited together, so a higher proportion of the offspring will have their parents genotype and phenotype.
if you do a cross and the ratios you find don’t match those provided, there is autosomal linkage

Question 24

what is epistasis?

Answer 24

when the allele of 1 gene masks the expression of the alleles of other genes

Question 25

what do epistatic genes do?

Answer 25

the phenotypic ratios are different to how expected, if a certain (epistatic) allele is present then other alleles are not expressed and so aren’t counted in he ratio

Question 26

what is the chi-squared test?

Answer 26

a statistical test that’s used to see if the results of an experiment support a theory

Question 27

how to carry out a chi-squared test?

Answer 27

make a null hypothesis - no significant difference between observed and expected
use the theory to predict the expected result, compare to observed results
carry out test and compare, the outcome will support or reject null hypothesis

Question 28

what is the Chi-squared formula?

Answer 28

sum of (O-E)^2/E

Question 29

how to find if there’s a significant difference between O and E?

Answer 29

compare X^2 value to critical value
if X^2 > critical value = significant difference
X^2 < critical value = no significant difference, difference due to chance

Question 30

how are genes inherited?

Answer 30

genes are inherited by both parents, in sexual reproduction by fusion of gametes
2 copies of each gene are inherited, 1 dominant, 1 recessive

Question 31

What kind of alleles are blood types?

Answer 31

A and B are codominant
O is recessive
only 2 alleles may be present in the loci

Question 32

what is haemophilia?

Answer 32

when a mutated allele results in a non-functional protein used in the clotting process
slow persistent internal bleeding
it can be treated by giving patient the normal protein