Unit 5 - Inheritance + Populations

Question 1

Definition of chromatin?

Answer 1

Made of DNA and histone proteins

Question 2

Definition of chromosome?

Answer 2

Made of chromatin. Each species has a different number of them and they contain all the genes for an organism.

Question 3

Definition of gene?

Answer 3

A base sequence of DNA on a chromosome which codes for the amino acid sequence of a polypeptide or a functional RNA

Question 4

Definition of locus?

Answer 4

The fixed position of a gene on a particular chromosome

Question 5

Definition of an allele?

Answer 5

A different version of a gene

Question 6

Definition of a diploid cell?

Answer 6

A cell containing 2 sets (homologous pairs) of each chromosome in the nucleus.

Question 7

Definition of a haploid cell?

Answer 7

A cell containing one set of each chromosome in the nucleus.

Question 8

Definition of a genotype?

Answer 8

The generic constitution of an organisms.

Question 9

Definition of a phenotype?

Answer 9

The expression of the genetic constitution and its interaction with the environment.

Question 10

What is a mutation?

Answer 10

A change to the DNA base sequence and can change the genotype. If the mutation is in the gametes this can be inherited.

Question 11

What are homologous chromosomes?

Answer 11

They have the same genes, in the same gene loci, but can have different alleles. This is because one of the pair is maternal and the other is paternal.

Question 12

Definition of homozygous?

Answer 12

When the allele on each homologous chromosome is the same.

Question 13

Definition of heterozygous?

Answer 13

When the allele on each homologous chromosome is different.

Question 14

Homozygous dominant=2 dominant

Answer 14

Homozygous recessive=2 recessive

Question 15

Definition of recessive allele?

Answer 15

Only expressed in the phenotype when 2 copies are present (homozygous)

Question 16

Definition of dominant allele?

Answer 16

Always expressed in the phenotype when present.

Question 17

What does a gene being expressed mean?

Answer 17

Expression of a gene means how it is transcribed into mRNA and then how mRNA is translated into a protein.

Question 18

P?
F1?
F2?

Answer 18

P - parental generation
F1 - offspring of the parents
F2 - offspring of the F1 generation

Question 19

Definition of monohybrid inheritance?

Answer 19

The inheritance of a single gene on an autosomal (a chromosome that isn’t a sex chromosome)

Question 20

Monohybrid crosses?

Question 21

What ratio do monohybrid crosses of heterozygous parents always produce?

Answer 21

3:1

Question 22

Why are actual results of genetic crossed rarely the same as predicted results?

Answer 22

-Fertilisation of gametes is random
-May be a small sample
-Some alleles may give a selective advantage/selective disadvantage/be a lethal allele
-Epistasis
-Linked genes

Question 23

What are codominant alleles?

Answer 23

They are alleles that are both expressed in the phenotype when they occur in a heterozygous individual.
Therefore there are 3 phenotypes, created by just 2 alleles
A gene letter is used and superscript letters are used for the allele

Question 24

Genetic diagram for codominant alleles?

Question 25

What is meant by multiple alleles?

Answer 25

If a gene has more than 2 alleles in a population. (You only have 2)

Question 26

Genetic diagram for multiple alleles?

Question 27

What is sex linked inheritance?

Answer 27

It is the inheritance of a gene found on the X or Y chromosome.

Question 28

What are the sex chromosomes: Of males? Of females?

Answer 28

Males - XY Females - XX

Question 29

Why are X and Y chromosomes not homologous pairs?

Answer 29

The Y chromosome carries only sex genes but the X chromosome carries both sex genes and genes controlling other body characteristics. Due to the Y chromosome being shorter, it does not have all of the same genes at the same gene loci as the C chromosome, so the C and Y chromosomes are not homologous pairs.

Question 30

Which sex is more likely to express the recessive alleles found on the sex chromosome and why?

Answer 30

Males because they only have 1 copy of the C chromosome so only need 1 copy of the recessive allele in their genotype to express the recessive phenotype, whereas females have 2 copies of the X chromosome so need 2 copies of the recessive allele in their genotype to express the recessive phenotype.

Question 31

Sex-linked inheritance crosses?

Question 32

What is a carrier?

Answer 32

Individuals who have 1 copy of a recessive allele for disease but do not express it in their phenotype because they’re heterozygous.

Question 33

What do sons inherit?

Answer 33

His X chromosome from his mother and his Y chromosome from his father

Question 34

What do daughters inherit?

Answer 34

X chromosome from his mother and an X chromosome from his father.

Question 35

What is a pedigree diagram?

Question 36

If a questions asks you what is the evidence that a phenotype is caused by a dominant or recessive allele?

Answer 36

Find 2 parents with the same phenotype who have offspring of the opposite phenotype. The parents must be heterozygous so whichever allele is expressed in their phenotype is dominant

Question 37

If a question asks you what is the evidence that the gene is found on the X chromosome?

Answer 37

Then normally only males will be affected in the diagram.

Question 38

What is dihybrid inheritance?

Answer 38

It is the inheritance of 2 different genes on different chromosomes at the same time.

Question 39

Dihybrid inheritance crosses?

Question 40

Dihybrid crosses of heterozygous parents always produce what phenotypic ratio?

Answer 40

9:3:3:1

Question 41

What is autosomal inheritance?

Answer 41

The inheritance of 2 or more genes carried on the same autosome (a chromosome that is not a sex chromosome). Assuming no crossing over all the genes found on the same chromosome will be passed to gametes during meiosis to offspring.

Question 42

Autosomal linked crosses?

Question 43

Explaining the results of autosomal linked genetic crosses?

Answer 43

-Say which alleles are linked based on the information given -State the gamete genotypes and phenotypes that would mainly be produced -Say that crossing over would produce some gametes with the non-linked genes together. State these gametes genotypes. -Say that fewer off spring with the non-linked phenotypes would be produced and state those phenotypes because crossing over is rare.

Question 44

Definition of epistasis?

Answer 44

When the allele of one gene affects or masks the expression of another gene.

Question 45

What is phenotype frequency?

Answer 45

How often a phenotype appears in a population.

Question 46

What is a genotype frequency?

Answer 46

How often a genotype appears in a population.

Question 47

What is an allele frequency?

Answer 47

How often a particular allele occurs within a population.

Question 48

What is the hardy Weinberg principle?

Answer 48

p^2 + 2pq + q^2 = 1. = genotype frequency p + q = 1. = phenotype frequency p^2 = homozygous dominant frequency 2pq = homozygous frequency q^2 = homozygous recessive frequency p = dominant allele frequency q = recessive allele frequency

Question 49

What are the assumptions made by Hardy-Weinberg?

Answer 49

1) Mating is random 2) There is no immigration so no new alleles are introduced 3) There are no mutations so no new alleles are created 4) There is no selection so no alleles are favoured or eliminated 5) The population is large