Class notes 3 - Genetics and Inheritance 1

Question 1

What is the definition of variation?

Answer 1

for any given trait (for any species) we see some variation within that trait.

Question 2

what are some examples of traits and their variations?

Answer 2

> eye colour - blue, green, brown, hazel

>hair texture- coarse, fine, wavy strait

Question 3

What is the definition of discontinuous (discrete) variation?

Answer 3

> traits that are linked to only one pair of genes - ‘single gene traits’.
gives rise to traits where it is a case of ‘either this or that’. There is no ‘in-between’
gives rise to bar graphs (e.g., taster or non-taster)

Question 4

What is continuous variation?

Answer 4

> There is no distinct groupings.
full spectrum of variation.
can be measured and quantified (assigned decimal values).
gives rise to curves of normal distributions.

Question 5

what does continuous variation relate to?

Answer 5

> traits that are influenced by 2 or more pairs of genes = polygenic traits (also referred to as ‘complex traits’).
Often results in bell curves

Question 6

What are the two factors that influence variation?

Answer 6

Environment and Genetic (meiosis and mutations)

Question 7

what are the two types of mutations studied?

Answer 7

gene (point) mutations

chromosome mutations

Question 8

what are homologous pairs?

Answer 8

homologous pairs are pairs of chromosomes that have the same chromosomes but 1 from each parent, i.e., same genes for the same traits.

Question 9

What happens in metaphase 1?

Answer 9

> homologous pairs line up with each other at the equator of the cell.
spindles are formed - extending from the centrioles

Question 10

what does the term letrad/bivalent mean?

Answer 10

the term is used with reference to homologous chromosomes pairing up during meiosis 1

Question 11

what happens in anaphase 1 ?

Answer 11

spindles contract and the homologous chromosomes are pulled towards opposite poles of the cell

Question 12

what happens in metaphase 2?

Answer 12

> chromosomes line up single file along the equator of the cell (as in mitosis).
spindles have attached to chromatids

Question 13

what happens in anaphase 2?

Answer 13

spindles contract and draw chromatids towards opposite poles of the cell.

Question 14

what is the end product of meiosis?

Answer 14

4 x n haploids = 1 of each chromosome.

Question 15

what is independent assortment?

Answer 15

homologous chromosomes have equal chance of migrating to either pole

Question 16

what is assortment?

Answer 16

chromosomes being ‘sorted’ into cells

Question 17

what is independent?

Answer 17

‘A’ and ‘a’ migrate independently of ‘B’ and ‘b’ or ‘C’ and ‘c’ or ‘D’ and ‘d’

Question 18

know the possible gametes thingo

Answer 18

2 to the power of four = 16 possible gamates.

2 to the power of n where n is the number of chromosomes

Question 19

What is a point mutations?

Answer 19

> change in the DNA sequence.

>may occur during DNA replication, where mistakes are made during the replication process.

Question 20

what are the types of point mutations?

Answer 20

substitution.
deletion
addition

Question 21

what is the mechanism and effect of a substitution mutation?

Answer 21

> a substitution of a single letter, for example, substituting T for G
this alters the mRNA sequence.
this alters the amino acid sequence.

Question 22

what happens when one amino acid is replaced with another?

Answer 22

a ‘mis-sense’ mutation

Question 23

what is an example of a substitution mutation?

Answer 23

sickle cell anemia. at codon 6, A is substituted by T. this substitution results in glutamic acid being replaced by valine.

Question 24

What is a deletion mutation?

Answer 24

a deletion mutation occurs when one or more nucleotides is/are removed from the DNA sequence.

Question 25

what type of mutation arises from a deletion mutation?

Answer 25

This type of mutation results in a ‘frame-shift’ mutation, to the left.

Question 26

what happens to the proteins in a deletion mutation?

Answer 26

Deletion mutations invariably result in no protein being formed.

Question 27

what is an addition mutation?

Answer 27

an addition mutation has the same effect as deletion mutations except that the ‘frame shift’ occurs in the opposite direction (right).

Question 28

how do ‘non-sense’ mutations occur?

Answer 28

if a substitution, deletion or addition mutation result in a ‘STOP’ sequence. No proteins are formed.

Question 29

what is a chromosomal mutation?

Answer 29

> chromosomal mutations can involve either the atleration of a large region of the chromosomes
OR it can involve unequal separation of during meiosis.

Question 30

What is an example of a disorder resulting from a deletion mutation?

Answer 30

Cystic Fibrosis. (however it can also be from a substitution mutation)

Question 31

what is a common type of chromosomal mutations?

Answer 31

a non-disjunction event

> when there is an unequal separation of homologous chromosomes during metaphase I.

Question 32

What is an example of a non-disjunction event?

Answer 32

Trisomy 21 (i.e., down syndrome) KNOW DIAGRAM!!!