Topic 7A: Genetics

Question 1

Gene =

Answer 1

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

Question 2

Allele =

Answer 2

A different version of a gene.

Humans carry 1 from each parent

Question 3

Genotype =

Answer 3

The genetic constitution of an organism (Bb or bb)

Question 4

Phenotype =

Answer 4

The expression of the genetic constitution and its interactions with the environment (characteristics)

Question 5

Dominant =

Answer 5

An allele whose characteristics appears in the phenotype even when there’s only one copy

Question 6

Recessive =

Answer 6

An allele whose characteristics only appears in the phenotype if two copies are present

Question 7

Codominant =

Answer 7

Alleles that are both expressed in the phenotype - neither is recessive

Question 8

Locus =

Answer 8

The fixed position of a gene on a chromosome

Question 9

Homozygote =

Answer 9

An organism that carries two copies of the same allele

Question 10

Heterozygote =

Answer 10

An organism that carries two different alleles

Question 11

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

How are humans diploid organisms

Answer 12

two sets of chromosomes - 2 alleles of each gene

Question 13

Genetic diagrams used to

Answer 13

predict the genotype and phenotype of the offspring if parents bred

Question 14

Monohybrid inheritance =

Answer 14

the inheritance of a characteristic controlled by a single gene

Question 15

Monohybrid crosses show

Answer 15

likelihood of different alleles of that gene being inherited by offspring

Question 16

Punnett square =

Answer 16

another way of showing a genetic diagram to predict genotype and phenotype of offspring

Question 17

Dihybrid crosses look at

Answer 17

how two different genes are inherited at the same time

Question 18

Phenotype ration in F2: Monohybrid

Answer 18

3:1 (D:d)

Question 19

Phenotype ration in F2: Dihybrid

Answer 19

9:3:3:1 (DD:Dd:dD:dd)

Question 20

Phenotype ration in F2: Codominant

Answer 20

1:2:1 (homozygous 1 allele: heterozygous allele: homozygous other allele)

Question 21

Female sex chromosomes

Answer 21

XX

Question 22

Male sex chromosomes

Answer 22

XY

Question 23

Sex linked characteristics =

Answer 23

allele that codes for the characteristic is found on the sex chromosome

Question 24

X linked genes =

Answer 24

genes that are only carried on the X chromosome

Question 25

Why are most genes on the sex chromosomes X linked genes

Answer 25

Y chromosomes smaller than X chromosomes so carries fewer genes

Question 26

Why do males only have one allele for sex linked genes

Answer 26

only 1 X chromosome

Question 27

Impact of males only having 1 sex linked gene

Answer 27

they only have 1 copy so express the allele even if recessive so more likely show recessive phenotypes for sex linked genes

Question 28

Genetic disorders caused by

Answer 28

faulty alleles on sex chromosomes

Question 29

Colourblindness =

Answer 29

sex linked disorder caused by faulty allele carried on the X chromosome

Question 30

Autosome =

Answer 30

any chromosomes that isn’t sex linked

Question 31

Why are autosomes genes said to be linked

Answer 31

on same autosome, together during independent segregation in meiosis 1 and alleles passed on to offspring together

Question 32

When wont autosomes be linked

Answer 32

if the go through ‘crossing over’ in meiosis 1 before segregation

Question 33

The closer together two genes are on autosome =

Answer 33

more closely linked because crossing over is less likely to split them up

Question 34

Impact on phenotype ratio if two genes are autosomally linked

Answer 34

more like monohybrid cross ratio than dihybrid because two autosomally linked alleles inherited together - higher proportional offspring with parents geno and phenotypes

Question 35

Importance of predicted phenotypic ratio

Answer 35

if different from the predicted we can identify autosomal linkage and epistasis

Question 36

Epistasis =

Answer 36

Allele of one gene masks the expression of alleles of other genes

Question 37

Epistasis example: widows peak and baldness

Answer 37

Doesn’t matter if you have the allele for widows peak if you have the baldness allele because no hair