Fundamentals

Question 1

what are mendels three laws? define each

Answer 1

1. law of dominance
2. law of segregation
3. law of independent assortment

Question 2

What is Mendel’s law of dominance?

Answer 2

if a dominant allele is present in the genotype it will be expressed in the phenotype

Question 3

What is Mendel’s law of segregation?

Answer 3

there are two copies of each gene (maternal and paternal) which are separated in meiosis, so each gamete has one copy of each gene and only one allele

Basically: gemetes’ ploidy number = 1

Question 4

What is Mendel’s law of independent assortment?

Answer 4

alleles for separate traits are inherited independently of each other

Question 5

What is the expected ration you would achieve for the F2 of a cross for a phenotypic trait with one dominant and one recessive parent in (P0)?

Answer 5

3:1
- 3 of the dominant phenotype
- 1 of the recessive phenotype

F1 would be the dominant phenotype (heterozygous)

Question 6

how can you check that the outcome of a cross is following the mendelian phenotypic ratios?

Answer 6

use a chi squared stat test to compare the expected ratio eg 3:1 or 9:3:3:1 with the observed ratio

Question 7

What significance level do you compare the chi squared value obtained to?

Answer 7

5% or 0.05

These are the same thing just expressed as a decimal and a percentage

Question 8

What is the null hypothesis when performing chi squared tests?

Answer 8

That the phenotypic ratio is as expected - therefore if the chi squared value is below the critical value at 5% significance, this is accepted

Question 9

Define Autosomal

Answer 9

When a trait is inherited independently of sex

Question 10

What does monogenic mean?

Answer 10

The trait is controlled by a single gene (rather than multiple)

Question 11

What is the ploidy number of gametes (sex cells that undergo meiosis)?

Answer 11

1n

Question 12

What stage of meiosis introduces genetic variance?

Answer 12

Prophase I

Question 13

What is the proper word for ‘crossing over’ over genetic info as seen in prophase 1?

Answer 13

Recombination

Question 14

What is a test cross used to find? What is done?

Answer 14

• It is used to determine the genotype of a dominant phenotype (whether it is homozygous or heterozygous dominant)
• You cross the individual in question with a homozygous recessive individual
• If all offspring is dominant, the parent genotype is likely homozygous dominant
• If offspring is mixed, then the parent genotype is heterozygous

Question 15

what is a reciprocal cross and why would you do one?

Answer 15

doing two crosses with the same traits being observed but swapping the sex of the parents to see if the trait is sex linked. eg cross a white eyed male fly with a wild type female and then cross a white eyed female fly with a wild type male. if each cross gives the same result it is an autosomal trait, if they give different results its a sex linked trait

Question 16

define genotype and phenotype

Answer 16

genotype is the alleles that the individual has for a particular gene. phenotype is the the expression of the genotype leading to the traits of an individual.

Question 17

describe crossing over/homologous recombination. what does this form? why does it occur?

Answer 17

crossing over occurs in prophase 1 when two homologous non-sister chromatids fuse at a chiasma and then break at this point, exchanging alleles in the process and producing recombinants. this increases genetic variation.

Question 18

what are monohybrid and dihybrid crosses? what are the resulting genotypic ratios if the parents are heterozygous for both traits?

Answer 18

a monohybrid cross is used to examine one trait (ratio 3:1 )but a dihybrid cross examines two unlinked traits (ratio 9:3:3:1).

Question 19

what can be inferred about two genes if a 9:3:3:1 ratio isn’t produced from a dihybrid cross where the parents are heterozygous for both traits.

Answer 19

the genes must be linked and this means they are on the same chromosome and are most likely to be found close together

Question 20

list the four types of large, chromosomal mutations that can occur

Answer 20

1. Duplication
2. Deletion
3. Inversion
4. Translocation

Question 21

give three ways that a large chromosomal deletion can occur and give a description of each

Answer 21

1. Transposons: ‘jumping DNA’ some transposition events cause a region of the genome to be deleted when the transposon moves
2. Incorrect DNA repair: sometimes 2 broken pieces of DNA are joined together missing another bit of the sequence inbetween
3. Non-disjunction: chromosomes may not seperate properly during meiosis and so the individual has monosomy (one less chromosome than there should be)

Question 22

What is the name of the condition we need to know where a deletion of part of a chromosome occurs?

Answer 22

Cri du chat syndrome

Means cry of the cat in French

Question 23

describe the banding system of chromosomes

Answer 23

1. chromosome number
2. arm (p arm - small arm (petite) q arm- long arm)
3. region
4. band
5. sub-band

regions, bands and sub-bands are numbered from the centromere outwards

p for petite!

Question 24

what is the significance of duplications when both copies are retained?

Answer 24

• They can lead to new phenotypes - opportunity for phenotypic novelty which may provide an evolutionary advantage
• One copy of the gene may evolve a new function leading to diversification of species
• Both copies may alternatively share the original function between them

Question 25

what are copy number variations (CNVs)

Answer 25

short repeated dna sequences throughout the genome with variable number of repeats in each individual eg. tandem repeats ## Footnote 5-10% of the genome

Question 26

what are the three types of tandem repeats?

Answer 26

- Tandem repeats: a DNA sequence is duplicated and the new sequence is found next to the original sequence - Reverse tandem repeats: where the duplicated sequence is found next to the original sequence but has been inverted - Terminal tandem repeats: when a sequence found at the end of a chromosome is duplicated.

Question 27

What is the condition caused by a duplication mutation that we need to know?

Answer 27

Trisomy-21 (Down syndrome)

Question 28

What is the difference between a conservative and non-conservative mutation?

Answer 28

- Conservatove = the function of the gene has been retained despite the mutation - Non-conservative = the function of the gene has not been retained

Question 29

What is the condition caused by translocation that we need to be aware of?

Answer 29

The Philadelphia chromosome - Translocation between chromosomes 9 and 22 - Causes cancer

Question 30

What is a slient mutation?

Answer 30

Where a single nucleotide changes, but the amino acid produced in the protein chain still remains the same ## Footnote Protein made is therefore the same too

Question 31

What is a missense mutation?

Answer 31

Where a change to the nucleotide sequence occurs and the amino acid translated **changes**. The sequece of the protein therefore changes too.

Question 32

what is the difference between a pericentric inversion and a paracentric inversion

Answer 32

a pericentric inversion doesn't include the centromere and a paracentric inversion does.

Question 33

What is a nonsense mutation?

Answer 33

- Where the nucleotide sequence is changed, instead producing a stop codon - This results in a truncated protein - The allele may lose its function if this occurs

Question 34

why do inversions and translocations impact meiosis?

Answer 34

they move the position of genes within the chromosome so that when the chromosomes pair up for homologous recombination the homologous genes are not aligned properly

Question 35

name the three types of translocation

Answer 35

- intrachromosomal (within a c'some) - interchromosomal(between c'somes) - reciprocal (when genetic informatio is exchanged - can only happen with interchromosomal)

Question 36

what can translocations lead to?

Answer 36

leads to gene fusions which can also result in protein fusions which can impact protein function or give it a new function.

Question 37

what does it mean that the genetic code is redundant/degenerate?

Answer 37

only the first two bases determine the amino acid and the third base can be variable. there is more than one codon for the same amino acid.

Question 38

what is haploinsufficiency

Answer 38

when there is only one copy of a gene due to a deletion for example, and there is not enough protein being produced as a result.

Question 39

What is disjunction?

Answer 39

The normal separation or moving apart of chromosomes toward opposite poles of the cell during cell division | Non-disjunction is the opposite where this does not occur correctly

Question 40

What are indels?

Answer 40

Changes in DNA sequences where one or more nucleotide bases are added/removed (insertion/deletion)

Question 41

How did Morgan's experiments confirm the chromosomal theory of inheritance?

Answer 41

- Found a male white-eyed fly - Crossed with wild type female - Discovered sex linkage

Question 42

What is linkage?

Answer 42

The tendency of genes that are closer together on a chromosome to be inherited together

Question 43

What does variation in recombination frequency tell you?

Answer 43

It indicates the actual distances separating the genes on the chromosomes ## Footnote The further the distance between the linked genes, the greater the chance of crossover and therefore recombination

Question 44

What is the equation for the recombination frequency?

Answer 44

RF = number of recombinant progeny / total number of progeny x 100

Question 45

How can you tell whether a gene is on a sex chromosome or an autosome?

Answer 45

- If mostly males are affected, it is sex-linked - If equal affliction, it is likely autosomal

Question 46

What is a polygenic trait?

Answer 46

A trait controlled by multiple genes

Question 47

What is incomplete dominance?

Answer 47

Both alleles are expressed in the phenotype, ususally leading to an intermediate or different phenotype

Question 48

What causes oculocutaneous albinism?

Answer 48

Mutations in tyrosinase to the OCA gene - causes melanin to be expressed abnormally | Most types of albinism are actually x-linked

Question 49

What is co-dominance?

Answer 49

Neither allele is dominant or recessive - both are equally expressed in the phenotype

Question 50

What is the difference between co-dominance and incomplete dominance?

Answer 50

- Co-dominance = expressed alongside eachother - think of it like a patchwork pattern (e.g. A + B blood = AB child) - Incomplete dominance = expressed as a blend of eachother - think of it like mixing paint colours (e.g. white + red snapdragon = pink offsping)

Question 51

What is an epistatic gene? Give an example of an epistatic gene

Answer 51

- An epistatic gene is a gene that modulates the expression of anothe gene - regardless of dominance - Example: coat colour in labradors

Question 52

What is haplosufficiency?

Answer 52

One functional copy of the gene is enough to make a nromal phenotype

Question 53

What is an allelic series?

Answer 53

A range set of difference alleles fro the same gene

Question 54

What is sex linkage?

Answer 54

- The shorter male Y chromosome has less genetic info - It therefore has fewer copies of certain genes - If they recieve a mutated copy of one gene, they must express this phenotypically if the Y chromosome does not posess a second copy

Question 55

What kind of inheritance applies to mitochondrial/chloroplast genes?

Answer 55

Non-Mendelian ## Footnote This is because organelle transmission doesn't follow Mendelian laws

Question 56

Ras is a very infamous ocnogene. What is the common gain of fucntion mutation occurring in Ras?

Answer 56

G12D missense mutation | Glycine at posititon 12 --> aspartate (D)

Question 57

What are most gain of function alleles?

Answer 57

Dominant - their phenotype is displayed

Question 58

What are most loss of function alleles?

Answer 58

Recessive - a single copy of the gene doesn't cause a phenotype | You can therefore have carriers of thistype of mutation

Question 59

What is the heterozygote advantage?

Answer 59

The fitness of the heterozygote is higher than the fitness of the homozygote - e.g. malaria and sickle cell disease CARRIERS ## Footnote Carriers dont have the disease, and are less likely to contract malaria. Homozygotes are less fit for survival whther they are wild type or whether they have sickle cell

Question 60

What is pleiotropy

Answer 60

Where one gene can have multiple effects of an organism's phenotype ## Footnote e.g. sickle cell disease allele causes: the disease, provides malaria resistance, production of abnormal beta-globin, reduced RBC at high altitiudes

Question 61

What is an amorph?

Answer 61

A mutant allele that has completely lost its function that produces a non-functional protein or no protein at all ## Footnote e.g. to have cystic fibrosis you must have 2 amorphic copies of the gene

Question 62

What is a hypomorph?

Answer 62

A mutant allele that results in a partially functional protein | less effective than wild type, more effective than an amorphic allele

Question 63

What is the difference between a transition and a transversion?

Answer 63

- Transition: substitute one purine for another, or one pyrimidine for another - Transversions: substitute a purine for a pyrimidine or vice versa

Question 64

Which are the purines and which are the pyrimidines?

Answer 64

- Purines: A and G - Pyrimidines: C and T ## Footnote Purines are the big ones, pyrimidines are the smaller ones

Question 65

Why is the substituation of a purine for an pyrimidine an issue?

Answer 65

A p[urine + pyrimidine is the perfect size. 2x pyrimidines would be too small, and 2x purines would be too big for DNA

Question 66

What is the penetrance of an allele?

Answer 66

The percentage of individuals with a given allele who exhibit the phenotype associated with that allele

Question 67

What can alter the penetrance of an allele?

Answer 67

- Interacting genes in the rest of the genome - e.g. modifiers, epistatoc genes, suppressors - Influence of the environemnt - e.g. how twins look more different based on the environment they grown up in

Question 68

What is expressivity?

Answer 68

The degree to which an allele is expressed at the phenotypic level | Measures the intensity of the phenotype ## Footnote Interacting genes and the environment both influence the expression of the phenotype