3.7.1 inheritance

Question 1

what is a gene?

Answer 1

a section of DNA that codes for a polypeptide/protein.

Question 2

where is a gene located?

Answer 2

at a specific locus on a chromosome.

Question 3

what is a chromosome?

Answer 3

contains many genes made of a long DNA molecule.

Question 4

what is an allele?

Answer 4

a version of a gene, as genes can exists in different versions.

Question 5

what is important about the location of alleles?

Answer 5

alleles of the same gene have slightly different base sequences but occupy the same locus.

Question 6

what is a locus?

Answer 6

a section of a chromosome where a gene is located.

Question 7

what’s the difference between a loci and locus?

Answer 7

locus is singular (a specific position of a gene on a chromosome) and loci is plural (multiple positions of genes on chromosomes).

Question 8

how many sets of chromosomes does a diploid organism have and how many is in their gametes?

Answer 8

diploid organism has two sets of chromosomes (in homologous pairs) and therefore has two copies of each gene. they produce haploid gametes that only carry one copy of each gene.

Question 9

what does homozygous mean?

Answer 9

individuals with identical/the same allele for a gene.

Question 10

what does heterozygous mean?

Answer 10

individual with different alleles for a gene.

Question 11

what is the genotype?

Answer 11

the genetic composition of an organism, all the alleles an organism possesses.

Question 12

what is a phenotype?

Answer 12

the observable characteristics determined by genotype and the environment.

Question 13

what is a dominant allele?

Answer 13

an allele that is always expressed in the phenotype: expressed in both homozygous and heterozygous individuals.

Question 14

what is a recessive allele?

Answer 14

only expressed in the phenotype if no dominant allele is present: only expressed when present in a homozygous individual.

Question 15

what is co dominance?

Answer 15

when both alleles in a heterozygous genotype are expressed: features of both alleles are expressed in the phenotype.

Question 16

what is mendel’s first law linked to monohybrid crosses?

Answer 16

each organism has two alleles for a gene and these speerate during gametes formation (meiosis) so each gametes contains one allele. fertilisation restores the pair of alleles.

Question 17

what is monohybrid inheritance?

Answer 17

the tracking the inheritance of one gene with two alleles.

Question 18

what genetic diagram is used to present monohybrid crosses etc?

Answer 18

punnet square.

Question 19

why may observed ratios in offspring differ from predictions?

Answer 19

due to random fertilisation of gametes.

Question 20

what can you determine the genotype of an individual showing the dominant phenotype?

Answer 20

a test cross with a homozygous recessive.

Question 21

what does a monohybrid test cross with all offspring showing the dominant phenotype tell you?

Answer 21

unknown genotype homozygous dominant.

Question 22

what does a monohybrid test cross with 50% dominant and 50% recessive tell you?

Answer 22

unknown genotype is heterozygous.

Question 23

what does a dihybrid test cross with no recessive phenotypes tell you?

Answer 23

unknown genotypes is homozygous dominant for both genes.

Question 24

what does a dihybrid test cross with at least one recessive phenotypes for one gene only tell you?

Answer 24

unknown genotype is heterozygous for one gene and homozygous dominant for the other.

Question 25

what does a dihybrid test cross with at least one recessive phenotypes for both genes tell you?

Answer 25

unknown genotype is heterozygous for both genes.

Question 26

what is linkage?

Answer 26

genes that are inherited together because they are on the same chromosome.

Question 27

what are the two types of linkage?

Answer 27

sex linkage and autosomal linkage.

Question 28

what is a women's sex chromosome?

Answer 28

two copies of the X chromosome: XX.

Question 29

what is a man's sex chromosome?

Answer 29

one X chromosome and one shorter Y chromosome: XY.

Question 30

which chromosome number is sex chromosomes?

Answer 30

23.

Question 31

where are sex-linked genes located?

Answer 31

on the X chromosome (rarely on the Y).

Question 32

why are males more likely to express recessive sex-linked traits?

Answer 32

as they only have one copy of X-linked genes.

Question 33

why can females be carriers of sex-linked traits?

Answer 33

as they have two copies of X-linked genes.

Question 34

what is a dihybrid cross?

Answer 34

tracks the inheritance of two genes simultaneously.

Question 35

genetic diagrams of dihybrid crosses follow a similar structure but they include:

Answer 35

more genotype combinations and more phenotype combinations.

Question 36

where does autosomal linkage occur?

Answer 36

in the autosomes.

Question 37

what are autosomes?

Answer 37

any chromosome that is not a sex chromosome.

Question 38

what is autosomal linkage?

Answer 38

two or more of the gens on the sea chromosome doe not assort independently during meiosis. these genes are linked and stay together ion the original parental combination: they will not dependently segregate during meiosis.

Question 39

autosomal linkage: why is there sometimes unexpected phenotypes?

Answer 39

due to crossing over.

Question 40

how can were work out how close together genes are on a chromosomes?

Answer 40

by the cross over value.

Question 41

how do you work out the cross over value?

Answer 41

number of recombinant offspring/total number of offspring x 100

Question 42

the larger the cross over value...

Answer 42

the more distant the genes.

Question 43

autosomal linkage: why does crossing over sometimes not affect the genes?

Answer 43

as the genes are very close together on the chromosome.

Question 44

what is epistasis?

Answer 44

when one gene affects the expression of another gene.

Question 45

what is the purpose of the chi squared test?

Answer 45

to determine whether or not there is a significant difference between the observed and expected results in an experiment.

Question 46

chi squared test: if difference in results are significantly different...

Answer 46

this suggests the presence of a factor that isn't being accounted for.

Question 47

chi squared test: if difference in results is not significantly different...

Answer 47

only differences that are observed are due to chance alone.

Question 48

what does the critical value depend on?

Answer 48

probability level (typically 0.05/5%) and the degrees of freedom.

Question 49

how do you work out the degrees of freedom?

Answer 49

number of classes - 1

Question 50

what criteria must be met for chi squared test?

Answer 50

1. large sample size. 2. data must be discrete values. 3. only raw counts, not percentages etc.

Question 51

if chi squared value ≳ critical angle...

Answer 51

significant difference not due to chance, so reject null hypothesis.

Question 52

if chi squared value < critical angle...

Answer 52

significant difference due to chance, so accept null hypothesis.