Molecular Biology & Genetics 5 - Mendel's Genetics, Extended + X-Linked Traits + Recombination

Question 1

What did people think prior to Mendel’s discoveries?

Answer 1

When two different traits reproduced together they would just blend

Question 2

What did Mendel find?

Answer 2

Traits didn’t blend and that some traits are dominant when crossed with different alleles of the same trait

Question 3

How is dominance shown?

Answer 3

When two individuals pure breeding for the dominant and recessive traits are crossed all of the offspring exhibit the dominant trait

Question 4

What is F1?

Answer 4

1st Filial generation

Question 5

What happens when two of the F1 offspring are crossed?

Answer 5

The recessive trait may appear again in a 3:1 ratio

Question 6

What is a monohybrid cross?

Answer 6

When one trait is being examined in the cross

Question 7

What was the first of Mendel’s Conclusions?

Answer 7

Information passed on from parents to offspring if information is packaged as discrete particles. Mendel called these factors. We now call them genes

Question 8

What was the second of Mendel’s Conclusions?

Answer 8

It also appears that individuals have 2 copies of each gene, one inherited from the mother and the other from the father. Genes controlling a trait can differ- these different forms of a gene are called alleles

Question 9

What happens in a pungent square?

Answer 9

The female and male gametes are crossed to show the potential offspring

Question 10

What is the genotypic ratio of a cross of 2 heterozygous individuals?

Answer 10

2 homozygous (1 dominant & 1 recessive) and 2 heterozygous

Question 11

What is the phenotypic ratio of a cross of 2 heterozygous individuals?

Answer 11

3:1 because the difference between homozygous dominant and heterozygous cab’t be determined

Question 12

What is the aim of a test cross?

Answer 12

To find out whether an individual with the dominant trait is homozygous dominant or heterozygous

Question 13

How is a test cross done?

Answer 13

By crossing the unknown individual with a homozygous recessive individual and observing the results

Question 14

What happens when the unknown individual in a test cross is homozygous dominant?

Answer 14

All offspring show the dominant phenotype so the plant must be homozygous. However, a large amount of repeats must be done to ensure this

Question 15

What happens when the unknown individual in a test cross is heterozygous?

Answer 15

Half of the offspring have the dominant trait and half have the recessive so the plant must be heterozygous

Question 16

What is Mendel’s 1st Law?

Answer 16

The law of segregation

Question 17

What is Mendel’s 2nd Law?

Answer 17

The law of independent assortment

Question 18

What are Mendel’s laws explained by?

Answer 18

Chromosomal behaviour during meiosis

Question 19

What is the law of segregation?

Answer 19

Genes segregate at meiosis so that each games contains only one of the two possessed by the parent

Question 20

What is the law of independent assortment?

Answer 20

Alleles of different genes assort independently during gamete formation

Question 21

Genes on chromosome can align…

Answer 21

in many different ways

Question 22

Separation of genes is not…

Answer 22

influenced by the movement of any other genes

Question 23

What is a dihybrid cross?

Answer 23

When two traits are being examined in the cross

Question 24

What ration is given by a dihybrid cross?

Answer 24

A 9:3:3:1 ratio

Question 25

What is the product rule?

Answer 25

Independent events are multiplied to get the probability of them all occurring

Question 26

What is the sum rule?

Answer 26

Mutually exclusive events are added to get the probability of them all occurring

Question 27

What is polymorphic?

Answer 27

When one gene has many alleles and therefore many phenotypes

Question 28

How many alleles can an individual have for a polymorphic gene?

Answer 28

Only 2, one on each homologous chromosome

Question 29

What is incomplete dominance?

Answer 29

When the F1 generation has an intermediate phenotype of the two parents. It seems like blending but heterozygous individuals just show incomplete dominance (dominant allele isn't completely dominant over the recessive allele). The parental phenotypes may reappear in the F2 generation

Question 30

What are recessive alleles?

Answer 30

Like broken alleles which don't contribute to the phenotype like the dominant alleles do

Question 31

What is co-dominance?

Answer 31

Where both phenotypes exist side by side within the organism (are equally as dominant as each other)

Question 32

Can co-dominant alleles still have a recessive allele?

Answer 32

Yes, alleles can be co-dominant to each other and both dominant over the recessive allele

Question 33

What are polygenic traits?

Answer 33

Traits of which the phenotype is controlled by many genes which have an additive effect.

Question 34

How do polygenic trait characters appear?

Answer 34

Continuous or quantitative

Question 35

What distribution is typical of a polygenic trait?

Answer 35

Normal distribution

Question 36

What happens when more genes are involved in a polygenic trait?

Answer 36

There are more phenotypic classes

Question 37

What also effects phenotype?

Answer 37

The environment

Question 38

What does the environment do?

Answer 38

Smooth differences between phenotypes. Although the genetics doesn't change, the phenotype does. The greater the effect on the environment the less the grouping/categories of phenotypes

Question 39

What do sex-linked traits involved?

Answer 39

Genes on the sex chromosomes (X or Y) rather than autosomes

Question 40

What happens with the inheritance patterns of sex-linked traits?

Answer 40

They differ between males (XY) and females (XX)

Question 41

What does hemizygous mean?

Answer 41

Only a single copy of a gene in a diploid organism (e.g. males)

Question 42

What does it mean if a gene is linked to the X chromosome in a male?

Answer 42

They will inherit the trait as they only have one x chromosome

Question 43

How many genes are there in humans?

Answer 43

Around 20,000

Question 44

How many chromosomes are there in humans?

Answer 44

23 pairs

Question 45

How many linked genes per chromosome?

Answer 45

Around 1000

Question 46

How are linked genes inherited?

Answer 46

Linked genes show biases towards the parental genotypes as they don't recombine

Question 47

How can we determine the order and location of genes within a chromosome?

Answer 47

By using the recombination frequencies

Question 48

What is the ratio expected when a heterozygote and a homozygote recessive cross in a test cross?

Answer 48

1:1:1:1

Question 49

Is a 1:1:1:1 ratio seen in a test cross with a heterozygote and a homozygote recessive?

Answer 49

No, not always. When the genes are linked most offspring will be the parental types with a few recombinants

Question 50

What should theoretically be given by meiosis?

Answer 50

All gametes having parental genotypes

Question 51

What do we get from meiosis?

Answer 51

Parental genotypes and some recombinants

Question 52

What explains recombination?

Answer 52

Crossing over

Question 53

What is recombinant frequency?

Answer 53

The proportion of recombinant genes

Question 54

What does distance have to do with crossing over?

Answer 54

The smaller the distance between two genes the less likely it is that a chiasma will form between them

Question 55

What has recombination frequencies around 50%

Answer 55

Distant (unlinked) genes which means they have around half recombinant and half parental genotypes

Question 56

What has recombinant frequencies of 0-50%?

Answer 56

Close (linked) genes

Question 57

What is the relationship between distance and recombination frequency?

Answer 57

Linear

Question 58

What can recombination frequency be used to work out?

Answer 58

How far away genes are on a chromosome in centimorgan (cM)

Question 59

What is the formula for working out how far away genes are on a chromosome?

Answer 59

cM = recombination frequency x 100

Question 60

What are the daughters from a cross with a female dominant homozygote (AA) and a father with trait (aY)?

Answer 60

All Carriers

Question 61

What are the sons from a cross with a female dominant homozygote (AA) and a father with trait (aY)?

Answer 61

All Normal

Question 62

What are the daughters from a cross with a female recessive homozygote (aa) and a normal male (AY)?

Answer 62

All Carriers

Question 63

What are the sons from a cross with a female recessive homozygote (aa) and a normal male (AY)?

Answer 63

All affected

Question 64

What are the sons from a cross with a female carrier (Aa) and a normal male (AY)?

Answer 64

Half normal, half affected

Question 65

What are the daughters from a cross with a female carrier (Aa) and a normal male (AY)?

Answer 65

Half normal (homozygous dominant), half carriers

Question 66

What are the sons from a cross with a carrier female (Aa) and a male with the trait (aY)?

Answer 66

Half normal, half affected

Question 67

What are the daughters from a cross with a carrier female (Aa) and a male with the trait (aY)?

Answer 67

Half carriers, half with trait