Inheritance (copy)

Define genotype

Genetic constitution of an organism

Define phenotype

The expression of genotype and its interaction with the environment

Define allele

Different forms of a gene

Define dominant and recessive allele

Dominant -allele of a gene that is expressed in phenotype even in the presence of an alternative alleles

Recessive-allele of a gene that is only expressed in phenotype if there is another identical allele present

Define codominant alleles

Both alleles of a gene are expressed in the phenotype of a heterozygote

Define homozygous

When an individual containers two identical alleles of a gene

RR or rr

Define heterozygous

When an individual contains two different alleles of a gene

What key info needed for a genetic cross diagram

Phenotype of parents

Genotype of parents

Genotypes of gametes each parent can produce

Punnets square-gametes on the outside

Genotype of offspring

Phenotype of offspring

Ratio of phenotypes of offspring

What is a mono hybrid cross

A genetic cross which just shows one gene

how Do you explain evidence from a pedigree chart to show that an individual is heterozygous

Individual has dominant phenotype therefore must have dominant allele

Offspring with recessive phenotype

Offspring with different phenotype to BOTH parents ,both parents must pass recessive allele and are displaying dominant must be heterozygous

Assuming a gene is not sex linked

What evidence do you look for im a pedigree chart to confirm that an allele is recessive

Name two parents who have the same phenotype as each other

Name offspring with different recessive phenotype

Parents must be heterozygous so pass recessive allele to their offspring

If the gene IS sex linked what is the evidence you look for in a pedigree chart to confirm that an allele is recessive

Name mother with dominant phenotype

Name offspring who has differnt phenotype -recessive

Mother must be heterozygous because has dominant phenotype so must have dominant allele passes recessive into offspring

• Any affected father would always pass condition to any daughter

What is meant by multiple alleles

When there are more than two possible alleles for a gene

Which three alleles exist for blood type

IA

IB

Io

What is sex linkage

When a gene is found on only the X chromosome

(Or Y)

If a gene is found on the X chromosome

The father with dominant phenotype will always have,,

Mother with recessive phenotype will always have….

Daughters with dominant phenotype,because father only has one copy of X chromosome and carries domiant allele that daughter inherit

Sons with recessive phenotype

Because mother must have two x chromsomes that both have recessive allele

Her sons will inherit the y chromsomes from dad and x chromsomes with recessive allele from mother

What evidence should you look for to show that a gene is not found on x chromsomes

Dominant father that has recessive daughter (dominant must be on y which she does not inherit)

Recessive mum that has dominant son (on Y)

What is a dihybrid cross

A genetic cross which shoes two genes

What is the genotype of a body cell of an individual that is heterozygous for both gene A and B

AaBb

Can form gametes

AB,Ab,aB,ab

How can you identify if autosomal linkage is occurring

• Use chi squared to check if the ratio of phenotypes in the offspring is significantly different to what you would expect

• Because some alleles linked

• Some gametes more likey to be found than others

• Some phenotypes will occur more or less often than expected

What is epistasis

When genes interact

Why would you use X2 test genetics

To work out the probability that the difference between the observed and expected ratios of phenotypes are due to chance

This helps you to understand more about the inheritance of certain characteristics and if there is any linkage between genes

What does it mean if the value of chi 2 is smaller than critical

More than 5%probability that the difference between observed and expected phenotypes ratios is due to chance

No significant difference

Assumed mechanism for inheritance is correct

What does it mean if chi squared is bigger than critical value p=0.05

Less than 5%probability that difference between observed and expected phenotype ratio is due to chance

significant difference in ratios

Something else affecting inheritance of characteristics

What could cause differences between the observed and expected phenotype ratios

Fertilisation and fusion of gametes is random

Sample size of offspring small

Some genes are linked

Epistasis

Some genotypes are lethal so those individuals die