Measuring Genetic Variability

Question 1

What are the two types of characters

Answer 1

Discrete characters → Mutually exclusive categories

e.g flower colour, fur colour

Quantitative → individuals vary continuously

e.g height, length, skin tone (melanism)

Question 2

What do genotypes affect

Answer 2

Most phenotypes are partly determined by genotype, which accounts for resemblance between parents and offspring

Question 3

What are genes, loci, and alleles

Answer 3

Gene = a discrete unit of inheritance

Locus (plural = loci) = a hypiothetical position / location of a gene

Allele = a variant in a gene

Example: the colour (phenotype) of a pea flower (which is dilpoid) is a discrete character, determined at a single locus, by genes of 2 possible alleles P or p

Question 4

What are dominant vs recessive alleles

Answer 4

Refers to the attributes of an Allele

A dominant Allele (uppercase letter) is one that only requires one copy to be present and expressed in the phenotype

A recessive Allele (lowercase letter) requires two copies to be expressed in the phenotype

Question 5

What is segregation

Answer 5

‘segregation’, During meiosis only one copy of each loci is contributed to the gamete (with equal probability)

Then the two gametes fuse into the diploid zygote with 2 alleles for each loci (one from each parent)

Question 6

What is homozygous vs Heterozygous

Answer 6

If they are both the same allele, that loci is Homozygous (PP)or(pp)

If they are different alleles, that loci is heterozygous (Pp)

Question 7

What is Mendelian inheritance

Answer 7

Dominance of some Alleles explains why some characteristics in a daughter population aren’t present in the parent generation

This pattern of inheritance discovered by Gregor Mendel

This simple pattern of inheritance of discrete phenotypes as “Mendelian”

Question 8

What is Independent assortment

Answer 8

Independent assortment is when during gametogenesis (meiosis) in a diploid germ cell, each copy/allele at a locus is equally likely to be passed to a given gamete.

Punnett Squares can be used to explicitly list all the genotype possibilities under independent assortment

Question 9

What happens when there are two loci in a gene

Answer 9

With something like a two loci genotype with (YyRr)

9 possible genotypes are possible

YYRR (1), YYRr (2), YYrr (2), YyRR (4), YyRr (1), Yyrr (2), yyRR (1), yyRr (2), yyrr (1)

with four possible phenotypes

YR, Yr, yR, yr

Question 10

what are the two important stats

Answer 10

1. mean - the average or ‘middle’ value
2. variance - the dispersion or ‘spread’

Question 11

What is the mean of a discrete variable of character equivalent to

Answer 11

Mathematically, the mean of a discrete variable of character is equivalent to the proportion (a number that ranges from 0 - 1)

Applied to any given genotype of allele, the population mean is simply the proportion, referred to as genotype frequencies and allele frequencies

Question 12

How do you calculate allele frequency

Answer 12

Allele frequencies are denoted p and q

The allele frequency is usually calculated by

P = (2PP + Pp) / (PP+Pp+pp)

p = (2pp + Pp) / (PP+Pp+pp)

Question 13

What happens in quantitative characters

Answer 13

For many continuously varying (or quantitative or polygenic) characters many loci contribute to phenotype with each locus possibly having many possible alleles.

Question 14

What are Phenotypic vs Genetic variances

Answer 14

Phenotypic variance: a measure of the total observable variation among individuals

Genetic variance: a measure of the genetic contribution to the difference among individuals

Question 15

What is Heritability

Answer 15

Heritability h^2 is the ration of

Genetic variance / phenotypic variance

measure of average parent-offspring resemblance

Question 16

What happened in 1858

Answer 16

In 1858 Darwin and Wallace both announced their co-discovery of descent with modification

Question 17

How do genes tie into evolution

Answer 17

Evolution is the natural outcome of unequal reproduction among individuals that bear heritable characters

The Inheritance of characters is based in genetics

Question 18

How was blending inaccurate

Answer 18

But this model was not always accurate on its predictions as offspring often had the characteristic of one of their parents and characters were not all converging on the average since variation persists

Question 19

What was the blending genetic model

Answer 19

Up to the 1800s inheritance was not understood. Though cells had been discovered the function of the nucleus and its contents was not known.

A prevailing model at the time was based on “blending” where offspring would be an intermediate of parental characters.

Question 20

What was Gregor Mendel theory

Answer 20

The Particulate hypothesis
is the idea that parents pass on discrete heritable units called genes.

Gregor Mendel correctly inferred the mechanism of inheritance, despite not being able to “see” genetic material and DNA was not discovered

Question 21

Direct a genome

Answer 21

In a diploid genome the genome is divided into loci (a specific part of the genome)

Each loci will have two alleles, one from each parent.
More than two Alleles are possible for each Loci, each Allele is a different option, example eye colour

Question 22

What are homozygous vs heterozygous

Answer 22

If they are both the same Alleles the Loci is Homozygous

If they are two different Alleles the Loci is Heterozygous

Question 23

What does lowercase vs uppercase mean with alleles

Answer 23

Dominant = uppercase
Recessive = lowercase

Question 24

What is the principle of Independent assortment

Answer 24

The allele is passed at one loci has no bearing on which allele is passed on at another loci

Question 25

Imagine that in pea plants the colour of a flower is based on a single locus, where P = Purple, and p = white
What are the possible genotypes and phenotypes

Answer 25

PP = purple, Pp = purple, and pp = white

In this situation, two white flowered plant will always lead to another white flower.

• genotypes Pp is heterozygous
• and genotypes PP and pp are homozygous

Question 26

If two Pp individuals fertilized, the ration of possible genotypes in the offspring would be _____
and the ration of phenotypes would be _____

Answer 26

PP:Pp:pp = 1:2:1
Purple:white = 3:1

Question 27

What statistical attributes are Evolutionary geneticist concerned with

Answer 27

Evolutionary geneticists are primarily concerned with 2 statistical attributes of a population

1. mean - the average or “middle” value
2. Variance - the dispersion or “spread”

With Alleles (a discrete variable), the mean frequency of an allele is actually simply its proportion

Question 28

What is Co-dominance

Answer 28

Co-dominance is when the resulting characteristic in the offspring is a blend of the two parents

Ex: red+white flower → pink flower

This can happen when there are two dominant alleles both being expressed at the same time

R+W → 1/2R + 1/2W

Question 29

What can happen when there are more than 2 alleles for a loci

Answer 29

For some loci there are more than 2 alleles which influence the phenotype

for example in human blood, there is an A, B, and o allele. (A+B dominant, o recessive)

resulting in blood types A, B, o, and AB

Question 30

What is linkage

Answer 30

In reality independent assortment does not always hold

The closer loci and genes are to one another (physically on a chromosome) the more likely it is that these will be inherited together during meiosis.

Question 31

What is Epistasis

Answer 31

When a phenotypic effect of a gene/allele at one locus depends on the gene/allele at another locus

Ex

The effect of the B/b alleles on coat colour in laborador retrievers depends on the E/e locus. ee makes the coat yellow, if its Ee or EE than the B/b alleles influences the coat colour to be various browns

Question 32

What is Pleiotrophy

Answer 32

when phenotypic effects of a gene/allele at one locus affects more than one character

Question 33

What are quantitative characters

Answer 33

For some characters like human height, many loci contribute to the phenotype, with each locus having many possible alleles. They act roughly additively. This is why human height exists on a range.

These characters are called quantitative, and vary continuously

Question 34

What is variance

Answer 34

The variance is a value defined as the sum of each individuals squared deviation from the mean divided by the ideal number of individuals

(∑(n-n)^2 )/N

standard deviation

Question 35

what is the mean

Answer 35

the mean is the average or middle value

(∑n)/N

Question 36

What is h^2

Answer 36

Heritability, h^2, is the ration (or proportion) of

genetic variance / Phenotypic variance

roughly a measure of average parent offspring resemble

Genetic variance is a measure of the genetic contribution to the differences among individuals

Phenotypic variance is a measure of the total observable variability among individuals

Question 37

Besides genotypes what can effect Phenotypes

Answer 37

Other things that affect phenotypic variance include:

• environmental background
• indirect genetic effects
• Gene interactions (Epistasis)
• Epigenetic effects (Gene expression controlled outside of the nucleus)