inheritance and populations

Question 1

Define gene

Answer 1

A sequence of bases on a DNA molecule that codes for a protein which results in a characteristics

Question 2

Define allele

Answer 2

A different version of a gene with different base sequences and therefore different codes

Question 3

Define genotype

Answer 3

The combination of alleles present within the cells of an organism

Question 4

Define phenotype

Answer 4

The expression of the genotype results in observable biochemical characteristics and its interactions with the environment

Question 5

Define dominant

Answer 5

An allele whose characteristics is expressed in the phenotype even though there is only 1 copy of it (heterozygous)

Question 6

Define recessive

Answer 6

An allele whose characteristic only appears in the phenotype if 2 copies are present (homozygous)

Question 7

Define codominant

Answer 7

Alleles that are both expressed in the phenotype in heterozygous conditions

Question 8

Define locus

Answer 8

In the fixed position of a gene on a chromosome, alleles of a gene are found the at the same locus on each chromosome in a pair

Question 9

Define homozygote

Answer 9

An organism that carries 2 copies of the same allele

Question 10

Define heterozygote

Answer 10

An organism that carries two different alleles

Question 11

Define carrier

Answer 11

A person carrying an allele which is not expressed in the phenotype but that can be passed on to the offspring

Question 12

Define dipoloid organisms

Answer 12

Organisms that have 2 sets of chromosomes

Question 13

How many alleles per gene do diploid organisms carry

Answer 13

2

Question 14

Define gametes

Answer 14

They are sex cells that contain only 1 allele for each gene

Question 15

How many alleles per gene do gametes carry?

Answer 15

1

Question 16

Explain what happens when two gametes fuse together

Answer 16

• When gametes from two parents fuse together, the alleles they contain form the genotype of the offspring produced
• At each locus, the genotype can be homozygous or heterozygous.

Question 17

What do genetic diagrams predict?

Answer 17

Predict the genotypes and phenotypes of the offspring produced if two parents are crossed

Question 18

Define monohybrid inheritance

Answer 18

It is the inheritance of a phenotypic characteristic controlled by a single gene

Question 19

What do monohybrid crosses show?

Answer 19

They show the likelihood of the different alleles of a gene being inherited by the offspring of certain parents

Question 20

What do Punnet squares predict?

Answer 20

The genotypes and phenotypes of offspring

Question 21

Define dihybrid inheritance

Answer 21

Where two phenotypic characteristics are determined by 2 different genes present on 2 different chromosomes at the same time

Question 22

Define phenotypic ratio

Answer 22

It is the ratio of different phenotypes in offspring

Question 23

Why do you not get the expected phenotypic ratios?

Answer 23

1. Crossing over between chromatids produces different combinations of alleles
2. Independent assortment produces different combinations of maternal and paternal alleles

Question 24

What are the sex chromosomes in mammals?

Answer 24

• In females: XX
• In males: XY

Question 25

What is meant by sex-linkage

Answer 25

Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual

Question 26

Why are males more likely to express a recessive sex-linked allele?

Answer 26

• Most sex-linked alleles are located on the X-chromosome
• Males only get 1 copy of the allele, so will express this characteristic even if it’s recessvie
• Since females get 2 alleles, this is less likely

Question 27

Which parent do males inherit sex-linked characteristics from?

Answer 27

• Their mother since the Y chromosome can only come from their father
• The mother is heterozygous for sex-linked alleles, she is a carrier and may pass the trait on

Question 28

What are autosomes

Answer 28

Any chromosome that isn’t a sex chromosome

Question 29

Where are autosomal genes found

Answer 29

On the autosome

Question 30

What is meant by autosomal linkage?

Answer 30

Where 2 or more genes are located on the same (non-sex) chromosome

Question 31

Explain autosomal linkage

Answer 31

• Genes are on the same autosome and stay together during the independent segregation of chromosomes in meiosis I
• Their alleles will be passed on to the offspring together
• The closer together the loci are on the autosome, the more closely they are linked because crossing over is less likely to split them up

Question 32

What can prevent sex-linkage?

Answer 32

Crossing over because it seperates the genes on the autosome

Question 33

What is meant by epistatsis?

Answer 33

Where two non-linked genes interact, with one gene either masking or suppressing the other gene

Question 34

Define 2 types of epistasis

Answer 34

1. Recessive epistasis = two homozygous recessive alleles at the first locus mask expression of another allele at the second locus
2. Dominant epistasis = where 1 dominant allele on the first locus masks expression of multiple other alleles at the second locus

Question 35

What is the chi-squares test?

Answer 35

A statistical test to find out whether the difference between the observed and expected data is due to chance or a real effect

Question 36

What are the criteria for the chi-squared test?

Answer 36

1. Data placed in discrete categories
2. Large sample size
3. Only raw count data allowed
4. No data values equal 0

Question 37

How can we use a chi-squared test in relation to inheritance?

Answer 37

We can compare expected phenotypic ratios with observed ratios to test our understanding of how different genes and alleles are inherited

Question 38

What do you conclude when your x^2 value is larger than or equal to the critical value?

Answer 38

There is a significant difference between the observed and expected result (something else other than chance is causing the difference) and the null hypothesis can be rejected

Question 39

What do you conclude when your x^2 value is smaller than the critical value?

Answer 39

There is no significant difference between the observed and expected results so the null hypothesis can’t be rejected

Question 40

Define species

Answer 40

A group of organisms that can interbreed to produce fertile offspring

Question 41

Define a population

Answer 41

All the organisms of a particular species that live in the same place and can potentially interbeed

Question 42

Define gene pool

Answer 42

The range of different alleles existing for a particlar locus within a population

Question 43

Define allele frequency

Answer 43

The proportion of a certain allele within a gene pool

Question 44

What is the Hardy-Weinberg principle

Answer 44

Allows us to estimate the frequency of alleles in a population, as well as if allele frequeency is changing over time

Question 45

What does the Hardy-Weinberg principle predict

Answer 45

Predicts that the frequencies of alleles in a population won’t change from one generation to the next

Question 46

Under what conditions is the Hardy-Weinberg principle true?

Answer 46

• No mutations occur to create new alleles
• No migration in/out of the population
• No selection, so alleles are all equally passed on to the next generation
• Random mating
• Large population

Question 47

Explain the Hardy-Weinberg equation for calculating allele frequency

Answer 47

• The frequencies of each allele for a characteristic must add to 1.0
• The equation: p + q = 1
• Where p = frequency of dominant allele
• Where q = frequency of recessive allele

Question 48

Explain the Hardy-Weinberg equation for calculating genotype frequency

Answer 48

• Frequencies of each genotype for a characteristic must add to 1.0
• p^2 + 2pq + q^2 = 1
• Where p^2 = frequency of homozygous dominant
• 2pq = frequency of heterozygous
• q^2 = frequency of homozygous recessive