M6, C20 Patterns of Inheritance and Variation

Question 1

define genotype

Answer 1

genetic make-up of an organism

Question 2

define phenotype

Answer 2

observable characteristics of an organism

Question 3

define dominant allele

Answer 3

version of the gene that will always be expressed if present

Question 4

define recessive allele

Answer 4

version of a gene that will only be expressed if 2 copies of this allele are present in the organism

Question 5

define homozygous

Answer 5

2 identical alleles for a characteristic

Question 6

define heterozygous

Answer 6

2 different alleles for a characteristic

Question 7

Describe continuous variation

give an example

Answer 7

continuous variation - individuals in a population vary within a range - there are no distinct categories
eg. height

Question 8

describe discontinuous variation

give an example

Answer 8

discontinuous variation - when there are to or more distinct categories - each individual falls into only one of these categories
eg. blood group

Question 9

define codominant

Answer 9

alleles that are both expressed in the phenotype - neither one is recessive

Question 10

define locus

Answer 10

the fixed position of a gene on a chromosome

Question 11

what are punnett squares used for

Answer 11

show a genetic diagram

predict genotypes and phenotypes of offspring

Question 12

define sex linkage

Answer 12

genes when its locus is one of the sex chromosomes, X or Y

Question 13

determine the possible genotypes of an offspring whose mother is a carrier of haemophilia but the father is unaffected

Answer 13

N is normal
n is faulty

carrier mother’s genotypes: X^N and X^n
unaffected father’s genotypes: X^N and Y

from punnett square the results show the 4 possibilities as:
X^NX^N - 25% unaffected female
X^NY - 25% unaffected male
X^nX^N - carrier female
X^nY - affected male

Question 14

what are the chromosomes of females and males in mammals

what does this mean about inheritance of diseases which are transmitted to offspring during sex linkage

Answer 14

females - 2 X chromosomes
males - 1 X chromosome, 1 Y chromosome

the Y chromosome is smaller than the X chromosome and carries fewer genes. so most genes on the sex chromosomes are only carried on the X chromosome.

this means males often have one allele for sex-linked genes meaning they express the characteristic even if it’s recessive. they can’t be a carrier

Question 15

determine the possible genotypes for a cow offspring whose parents have genotypes RR and WW
R is red
W is white

what is this an example of?

Answer 15

punnett square shows the possible gneotypes are:
RW, RW, RW, RW
100% red/white cow

example of codominance

Question 16

define monohybrid inheritance

Answer 16

inheritance of a single characteristic controlled by different alleles

Question 17

define dihybrid inheritance

Answer 17

inheritance of 2 different characteristics caused by 2 genes

Question 18

what would you get if you cross two organisms each with 2 homozygous alleles

Answer 18

the offspring would be heterozygous for both alleles

Question 19

One parent has the genotype of NNGG and the other has the genotype of nngg.
what would the genotype be for the F1 offspring

Answer 19

F1 offspring means first generation

two homozygous parents makes a heterozygous offspring so

NnGg

Question 20

When you cross two heterozygous individuals what ratio would you expect to find for the phenotypes of the offspring

Answer 20

four possible phenotypes

9:3:3:1

Question 21

If you cross a heterozygous organism and a homozygous recessive organism, what ratio would you expect for the phenotypes of the offspring

Answer 21

four possible phenotypes
1:1:1:1
two alleles show complete dominance and are located on separate chromosomes

Question 22

In pea plants the dominant allele for seed shape is round shown by R and the dominant allele for seed colour is green shown by G.
The recessive alleles are r for wrinkled and g for yellow.
A round, yellow seed is crossed with a green, wrinkled seed.
Produce a full genetic cross diagram to show the ratio of 2nd generation offspring.

Answer 22

Two homozygous parents make a heterozygous offspring
So 1st generation offspring = RrGg
On each side of genetic cross diagram there should be the gametes of RG, Rg, rG and rg
You get 16 results of:
RRGG, RRGg, RrGG, RrGg, RRGg, RRgg, RrGg, Rrgg, RrGG, RrGg, rrGG, rrGg, RrGg, Grgg, rrGg, rrgg

Looking at the dominant and recessive alleles, this makes the ratio of 9:3:3:1 of the phenotypes:
9 round and yellow pea plants
3 round and green
3 wrinkled and yellow
1 wrinkled and green

Question 23

How would you split a parent with the genotypes RrHh into gametes

Answer 23

R with H
R with h
r with H
r with h

SO: RH, Rh, rH and rh

(the alleles come in pairs so Rr and Hh CAN’T go together)

Question 24

define autosomal linkage

Answer 24

when the genes that are linked are found on one of the other pair of chromosomes

Question 25

how do recombinants form | hint: meiosis

Answer 25

- When the chromosomes pair up in prophase 1 of meiosis, crossing over occurs between the non sister chromatids, resulting in an exchange of the genes - Some of the linked genes are separated - They will have a different combination than either of the parents, so are called recombinants - The closer the genes are on the chromosome, the less likely they are to separate

Question 26

what is recombination frequency

Answer 26

the measure of the amount of crossing over in meiosis

Question 27

what is the equation for recombination frequency what do the results show

Answer 27

number of recombinant offspring / total number of offspring 50% or more = no linkage (genes are on separate chromosomes) Less than 50% = there is gene linkage (random process of independent assortment has been hindered)

Question 28

what is the chi-squared test

Answer 28

tests whether the difference between the observed and expected results are due to chance or whether there is a significant difference and so your experiment or prediction you made must be wrong

Question 29

χ^2 = Σ(O-E)^2 / E | This is the chi-squared formula. What do all the parts stand for?

Answer 29

``` χ^2 = chi-squared O = observed results E = expected results ```

Question 30

once you have a result for the chi-squared test what do you do?

Answer 30

Work out the degrees of freedom by taking away 1 from the number of categories Then use the table. Look for the degree of freedom and 5% (0.05)

Question 31

what does it mean if the chi-squared value is less than the critical value?

Answer 31

there is no significant difference between observed and expected results more likely to be due to chance accept null hypothesis

Question 32

what does it mean if the chi-squared value is more than the critical value?

Answer 32

there is a significant difference between expected and observed results reject null hypothesis some other factor is causing the difference between observed and expected results

Question 33

what are the columns you need to have when completing a chi-squared test

Answer 33

``` Phenotype Ratio E (expected result) O (observed result) O-E (O-E)^2 (O-E)^2 / E ```

Question 34

define epistasis

Answer 34

the interaction of genes at different loci so that one gene locus masks or supresses the expression of another gene locus

Question 35

What is recessive epistasis?

Answer 35

Homozygous presence of a recessive allele prevents the expression of another allele at a 2nd locus. So if there is any recessive homozygous set of alleles (eg. aa), the other gene can't be expressed.

Question 36

What will the ratio of phenotypes be if you cross two purple flowers that are AaBb? aa means the flower will be white due to recessive epistasis

Answer 36

when you do the 16 punnet square you get the genotypes of: AABB, AABb, AaBB, AaBb, AABb, AAbb, AaBb, Aabb, AaBB, AaBb, aaBB, aaBb, AaBb, Aabb, aaBb, aabb All the ones with aa will be white. All the ones with a dominant A and bb will be pink. All the ones with a dominant A and Bb or BB will be purple. The ratio of purple:pink:white is 9:3:4

Question 37

What is the ratio of phenotypes you will get when you cross 2 heterozygous genotypes in recessive epistasis?

Answer 37

9:3:4

Question 38

What is dominant epistasis?

Answer 38

Dominant allele at one gene locus masks the expression of the alleles at a 2nd gene locus. So if there is any dominant gene in the set of alleles (eg. Dd or DD) then the other gene can't be expressed..

Question 39

What will the ratio of phenotypes be if you cross 2 white flowers (DdEe) in dominant epistasis? E = yellow flowers e = green flowers

Answer 39

when you do the 16 punnet square you get the genotypes of: DDEE, DDEe, DdEE, DdEe, DDEe, DDee, DdEe, Ddee, DdEE, DdEe, ddEE, ddEe, DdEe, Ddee, ddEe, ddee All the ones with any dominant allele of D mean no colours can be expressed. (Because of the dominant epistasis). All the ones with dd mean that a colour can be expressed so if the E is present it will be yellow but if it's ee it will be green. The ratio of white:yellow:green is 12:3:1

Question 40

What are the possible ratios of phenotypes you can get when you cross 2 heterozygous genotypes in dominant epistasis?

Answer 40

12:3:1 OR 13:3

Question 41

Describe the process of evolution by natural selection

Answer 41

- Individuals within a population vary due to different alleles. - New alleles created due to mutations in their genes. - Selection pressures like predation, disease or competition create a struggle for survival. - The individuals that are most suited to the environment (have an allele that increases chance of survival) survive, reproduce and pass on the advantageous allele. - A greater proportion of the next generation inherit the advantageous allele. - They in turn are more likely to survive, reproduce and pass on their genes. - The frequency of advantageous allele increases.

Question 42

define gene pool

Answer 42

the complete range of alleles present in the population

Question 43

define population

Answer 43

group of organisms of the same species living in a particular area