Genetic Variation

Question 1

Define mutations

Answer 1

A change in the genetic material of an organisim, usually in the DNA. They are a result of chance. Exposure to environmental factors called mutagens such as radiation or smoking can increase the chance of a somatic mutation occurring

Question 2

Define somatic mutations

Answer 2

Mutations that occur in all the cells in the body except the sperm cells or the egg cells, therefore impossible to pass onto offspring. For example lung cancer from smoking or melanoma.

Question 3

Define gametic mutations

Answer 3

Gametic mutations occur in the germ cells, meaning they are produced in the sex cells and can be passed onto offspring. An example in breast cancer being passed down the generations in a family.

Question 4

Define a homologous chromosome

Answer 4

They are pairs of chromosomes which are identical in length and shape and have the same genes. One of them is from the mother the other is from the father

Question 5

Define a diploid

Answer 5

The normal number of chromosome within a human body cell (46)

Question 6

Define a phenotype

Answer 6

a physical expression of the genotype, eg curly brown hair or green eyes

Question 7

Define a genotype

Answer 7

The combination of two different alleles eg Bb to make brown hair to become the phenotype

Question 8

What is a dominant and recessive allele

Answer 8

A dominant allele has a capital letter B to be the dominant genotype to be expressed, the recessive allele is the lower case b which are over run by dominant alleles unless all alleles are recessive (homozogous)

Question 9

Define Hetrozygous

Answer 9

Two different alleles which creat different genotypes, eg Aa

Question 10

Define homozygous

Answer 10

the same type of allele, eg bb or B

Question 11

Define an allele

Answer 11

Different forms of the same gene. Alleles are dominant and/or recessive

Question 12

what is co-dominance

Answer 12

both genes are dominant and both alleles are equally and independently expressed. This causes a mix and creates roan cows

Question 13

Define incomplete dominance

Answer 13

both genes are recessive eg rr wr. The result of it is the heterozygous alleles blend the two traits

Question 14

What is a gene pool

Answer 14

A set of all the genes or genetic information in any population, usualy of a particular species

Question 15

Define meiosis

Answer 15

The process of cell division that occurs in the ovaries and testes and makes the sex cells ova and sperm (gametes). Basically its the mixing of allele combination to form new ones, in two phases

Question 16

What is incomplete dominance

Answer 16

One allele does not completely dominate over the other and a new phenotype is made by blending the two genotypes together eg a red snapdragon flower and a white snapdragon flower crossed making a pink snapdragon offspring.

Question 17

what is a linked gene

Answer 17

genes located on the same chromosome and tend to be inherited together, this reduces genetic variation in the offspring when crossing over occurs.

Question 18

What is a monohybrid cross?

Answer 18

A cross of only one gene eg brown hair dominant (B) and black hair recessive (b) which makes a 2x2 punnet square with a 1:1 genotype/phenotype ratio

Question 19

Define a lethal allele

Answer 19

they are mutations of a gene that produce a non-functional gene product which may affect the organisms survival

Question 20

What is recombination

Answer 20

The exchange of alleles between homologous chromosomes as a result of crossing over. Recombinations increase the genetic variation in the offspring.

Question 21

What is crossing over

Answer 21

The exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in the offspring and larger genetic variation

Question 22

Define a homologous chromosome

Answer 22

A homologous chromosome is a pair and half of it comes from the mother and the other half comes from the father. Homologous chromosomes are similar, each carries the same genes in the same order, but the alleles for each trait may not be the same.

Question 23

natural selection: what is stabilising selection

Answer 23

phenotypic extremes are selected against, reducing variations in a populations, happens most the time in populations to prevent a difference in a form of function such as birth weight in infants

Question 24

natural selection: what is directional selection

Answer 24

the adaptive phenotype is shifted in one direction and one phenotype is favoured over the other, this could happen because of a change of environment

Question 25

natural selection: what is disruptive selection

Answer 25

Disruptive selection favours two phenotypic extremes at the expense of the intermediate form, increasing the variation in a population.

Question 26

What is a bottleneck

Answer 26

population bottlenecks occur when population numbers and diversity fall dramatically although a populations number may recover, often its genetic diversity does not

Question 27

What is a dihybrid cross?

Answer 27

A cross of two different genes in a punnet square, eg Rwrw which makes a genotype and phenotype ration of 9:3:3:1. When making a dihybrid cross on a punnet square, all combinations of alleles will be made eg Rw, Rw, rw, rw