genetics & inheritance

Question 1

what is a gene

Answer 1

a gene is a section of DNA, that codes for a specific amino acid

Question 2

what is an allele

Answer 2

a different version of the same gene

Question 3

what is a genotype

Answer 3

the genetic constitution of an organism

Question 4

what is a phenotype

Answer 4

the expression of this genetic constitution and its interaction with the environment

Question 5

what can alleles be

Answer 5

recessive, dominant or codominant

Question 6

what can the alleles be in a diploid organism

Answer 6

may be either homozygous or heterozygous

Question 7

define homozygous `

Answer 7

if the two copies of a gene are the same allele

Question 8

define heterozygous

Answer 8

if the two copies of a gene are different alleles

Question 9

give an example of each
homozygous dominant
heterozygous
homozygous recessive

Answer 9

BB

Bb

bb

Question 10

define codominant alleles

Answer 10

equally expressed within the phenotype

so they would start off with two equal pairs (homozygous) which would end up creating all heterozygous so in that sense they are equally expressed within the F1 generation

Question 11

what is the ratio for codominance

Answer 11

1:2:1

Question 12

what is the ratio for monohybrid

Answer 12

3:1

Question 13

define monohybrid

Answer 13

single characteristic

Question 14

what are multiple alleles

Answer 14

more than 2 alleles for the same gene, this produces hierarchy of dominance

Question 15

what is monohybrid inheritance

Answer 15

the inheritance of a single gene, which determines a single characteristic

Question 16

how are gametes indicated

Answer 16

by drawing a circle around the allele

Question 17

the fusion of gametes is…

Answer 17

random

Question 18

what is a gene pool

Answer 18

all the alleles within an interbreeding population (at a specific time)

Question 19

what are the 2 different types of hardy-weinberg equations

what do the letters represent

Answer 19

p + q - 1
p = dominant
q = recessive

p2 + 2pq + q2 = 1

p2 = homozygous dominant
2pq = heterozygous
q2 = homozygous recessive

Question 20

What does Hardy-Weinberg principle predicts that

Answer 20

The allelic frequencies (of a particular gene ) from one generation to the next will remain constant

if there is NO :
migration i.e, the gene pool is isolated and there is no flow of other alleles in or out
gene mutations
selection for or against a particular allele

in addition :
there should be a large population
mating within the population should be random (all individuals have an equal chance of mating)

important - highly unlikely that any natural population meet all these requirements

Question 21

state three causes of genetic variation

Answer 21

mutation
crossing over
independent segregation
random fusion of gametes

Question 22

what is meant by a genome

Answer 22

all the DNA in a cell
all the genes/alleles in a cell
the total number of DNA bases in a cell

Question 23

how do multiple alleles of a gene arise

Answer 23

mutations
which are different/at different positions in the gene

Question 24

what is meant by a recessive allele

Answer 24

only expressed in the homozygote

Question 25

in genetic crosses, the observed phenotypic ratios obtained phenotypic ratios obtained in the offspring area often not the same as the expected ratios suggest two reasons why

Answer 25

small sample size fusion of gametes is random linked genes; sex-lineage/ crossing over epistatis lethal genotypes

Question 26

define gene lineage

Answer 26

(genes/loci) on same chromosome

Question 27

define epistasis

Answer 27

the allele of one gene affects or masks the expression of another in the phenotype

Question 28

described why observed phenotypes don't match expected values

Answer 28

fertilisation is random OR fusion of gametes is random; small population/sample; selection advantage/disadvantage/lethal alleles;

Question 29

rules for dominant alleles

Answer 29

affected offspring MUST have at least one affected parent. unaffected parents ONLY have unaffected offspring. if both parents are affected and have an unaffected offspring, both parents must be heterozygous

Question 30

rules for recessive alleles

Answer 30

unaffected parents can have an affected offspring (if they are heterozygous)

Question 31

male offspring are more likely than females to show recessive sex-linked characteristics. explain why

Answer 31

(recessive) allele is always expressed in males females need two recessive alleles

Question 32

expected offspring phenotype ratios from heterozygous parents: monohybrid dihybrid epistasis autosomal linkage

Answer 32

dominant : recessive 3:1 9:3:3:1 9:4:3 or 15:1 or 9:7 3:1 (no x over) (no other pattern other than 4 phenotypes with recombination of alleles)

Question 33

State three causes of genetic variation

Answer 33

• Mutation • Crossing over • Independent segregation / assortment (of homologous chromosomes) • Random fusion of gametes / fertilisation / mating

Question 34

What is meant by a genome?

Answer 34

• (All) the DNA in a cell/organism; • ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’ • ‘the total number of DNA bases in a cell/organism’

Question 35

What is a gene pool?

Answer 35

• All the alleles in a population;

Question 36

How do multiple alleles of a gene arise?

Answer 36

• mutations; • which are different / at different positions in the gene;

Question 37

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why.

Answer 37

• Small sample size; • Fusion/fertilisation of gametes is random; • Linked Genes; Sex-linkage / crossing over; • Epistasis; • Lethal genotypes;

Question 38

What is meant by a recessive allele?

Answer 38

• Only expressed in the homozygote / not expressed in the heterozygote / not expressed if dominant present;1

Question 39

What does Hardy Weinberg’s equation predict

Answer 39

• The frequency/proportion of alleles (of a particular gene); • Will stay constant from one generation to the next/over generations / no genetic change over time; • Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration;

Question 40

Define gene linkage

Answer 40

• (Genes/loci) on same chromosome;

Question 41

Define epistasis

Answer 41

• The allele of one gene affects or masks the expression of another in the phenotype;

Question 42

Describe why observed phenotypes don’t match expected values

Answer 42

• Fertilisation is random • OR • Fusion of gametes is random; • Small/not-large population/sample; • Selection advantage/disadvantage/lethal alleles;

Question 43

Define codominance

Answer 43

• Both alleles expressed in the phenotype;

Question 44

Rules for Dominant alleles

Answer 44

• Affected offspring MUST have at least one affected parent. • Unaffected parents ONLY have unaffected offspring. • If both parents are affected and have an unaffected offspring, both parents must be Heterozygous

Question 45

Rules for recessive alleles

Answer 45

• Unaffected parents can have an affected offspring (if they are Heterozygous)

Question 46

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.

Answer 46

• (Recessive) allele is always expressed in males / males have one (recessive) allele; • Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;

Question 47

Expected offspring phenotype ratios from heterozygous parents: 1. Monohybrid 2. Dihybrid 3. Epistasis 4. Autosomal linkage

Answer 47

1. 3:1 2. 9:3:3:1 3. 9:4:3 or 15:1 or 9:7 4. 3:1 (no x over) (no other pattern other than 4 phenotypes with recombination of alleles)

Question 48

What is meant by the term phenotype

Answer 48

• (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s); • (Expression / appearance / characteristic due to) interaction with environment;

Question 49

Explain how a single base substitution causes a change in the structure of a polypeptide

Answer 49

• Change in (sequence of) amino acid(s)/primary structure; • Change in hydrogen/ionic/disulfide bonds; • Alters tertiary/30 structure;