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A-Level Biology > M6, C20 Patterns of Inheritance and Variation > Flashcards

M6, C20 Patterns of Inheritance and Variation Flashcards

1
Q

define genotype

A

genetic make-up of an organism

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2
Q

define phenotype

A

observable characteristics of an organism

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3
Q

define dominant allele

A

version of the gene that will always be expressed if present

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4
Q

define recessive allele

A

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

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5
Q

define homozygous

A

2 identical alleles for a characteristic

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6
Q

define heterozygous

A

2 different alleles for a characteristic

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7
Q

Describe continuous variation

give an example

A

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

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8
Q

describe discontinuous variation

give an example

A

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

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9
Q

define codominant

A

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

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10
Q

define locus

A

the fixed position of a gene on a chromosome

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11
Q

what are punnett squares used for

A

show a genetic diagram

predict genotypes and phenotypes of offspring

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12
Q

define sex linkage

A

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

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13
Q

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

A

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
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14
Q

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

A

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

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15
Q

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?

A

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

example of codominance

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16
Q

define monohybrid inheritance

A

inheritance of a single characteristic controlled by different alleles

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17
Q

define dihybrid inheritance

A

inheritance of 2 different characteristics caused by 2 genes

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18
Q

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

A

the offspring would be heterozygous for both alleles

19
Q

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

A

F1 offspring means first generation

two homozygous parents makes a heterozygous offspring so

NnGg

20
Q

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

A

four possible phenotypes

9:3:3:1

21
Q

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

A

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

22
Q

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.

A

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
23
Q

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

A

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)

24
Q

define autosomal linkage

A

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

25
Q

how do recombinants form

hint: meiosis

A
  • 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
26
Q

what is recombination frequency

A

the measure of the amount of crossing over in meiosis

27
Q

what is the equation for recombination frequency

what do the results show

A

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)

28
Q

what is the chi-squared test

A

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

29
Q

χ^2 = Σ(O-E)^2 / E

This is the chi-squared formula. What do all the parts stand for?

A 
χ^2 = chi-squared
O = observed results
E = expected results
30
Q

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

A

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)

31
Q

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

A

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

32
Q

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

A

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

33
Q

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

A 
Phenotype
Ratio
E (expected result)
O (observed result)
O-E
(O-E)^2
(O-E)^2 / E
34
Q

define epistasis

A

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

35
Q

What is recessive epistasis?

A

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.

36
Q

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

A

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

37
Q

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

A

9:3:4

38
Q

What is dominant epistasis?

A

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..

39
Q

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

A

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

40
Q

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

A

12:3:1
OR
13:3

41
Q

Describe the process of evolution by natural selection

A
  • 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.
42
Q

define gene pool

A

the complete range of alleles present in the population

43
Q

define population

A

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

A-Level Biology (23 decks)

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