Biology - INHERITANCE

What is the genotype of an organism?

the genes an organism posesses

What is the phenotype of an organism?

how the genotype is physically expressed and its interaction with the environment

what is a gene?

a section of DNA that codes for a polypeptide/protein in an organism

what is a locus?

the specific location of a gene on a chromosome

what is an allele

one of multiple different forms of a gene

what do homozygous and heterozygous mean in terms of alleles?

homozygous means both alleles are the same; heterozygous means they are different

what is a dominant allele?

an allele that is always expressed in the phenotype

what is a recessive allele?

an allele that is only expressed in the phenotype if it is homozygous

what does co-dominant mean?

when both alleles in a heterozygote contribute to the phenotype - both alleles are equally dominant

what is the chi squared test used for in genetics

to see if the difference between the observed value and the expected value is significant or not

how is a dominant allele represented in a genetic diagram

capital letter

why does autosomal linkage reduce variation?

pairs of alleles are inherited together

how is it possible for a female to be a carrier but not a sufferer of a sex linked condition?

has one copy of the defective recessive allele but the other, normal allele is dominant, so the recessive phenotype is not expressed

why do some males suffer from sex linked diseases?

their Y chromosome is missing some genes that are carried on their X chromosome, so some recessive alleles on the X chromosome are expressed alone , giving the disease phenotype

if a woman carrying an allele for colourblindness has a child with a man with normal vision, what is the chance that they will have a son who is colour blind?

50%

what is epistasis?

when the allele of one gene affects or masks the expression of another phenotype

how is mouse coat colour an example of epistasis?

Gene B determines the expression of gene A

What does F1 mean?

the first generation of a cross

what is the autosome?

chromosomes that aren’t the sex chromosomes (1-22)

what is dihybrid inheritance?

the simultaneous inheritance of 2 genes controlling separate characteristics

what is the expected ratio from a dihybrid cross of 2 heterozygous parents?

9:3:3:1

in incomplete dominance what phenotype is seen when a red flower is crossed with a white flower?

100% pink flowers

what is multiple alleles?

when there are more than 2 alleles eg human ABO blood group I^A I^B I^O (although there are 3 alleles only 2 can be present at any one time)

What is sex linkage?

genes located on the X and Y chromosomes that are inherited differently by males and females

give an example of an X linked genetic disorder

haemophilia

what is autosomal linkage?

when 2 or more genes are on the same autosome and tend to be inherited together and do not independently assort

what is the word equation for chi squared

chi squared = sum of (observed numbers O - expected numbers E)² /expected numbers E

how do you calculate degrees of freedom

number of classes/categories - 1

what is the critical value in the chi squared test?

p=0.05

when is chi squared significant

if the deviation is less than 0.05

when is chi squared not significant

if the deviation is more than 0.05

what is the wild type?

the phenotype of the typical form of the species as it occurs in nature

what is incomplete dominance

when both alleles are equally expressed

give an example of co-dominance

cattle coat colour
C^R C^R - red coat
C^WC^W - white coat
C^WC^R - roan coat - both red and white hairs present, not a blended colour

what is a recombinant phenotype

describes offspring with a new characteristic that wasn’t seen in either parent, resulting from crossing over during meiosis

reasons for recombinant phenotypes

independent assortment
crossing over
gene linkage

why can males never show the codominant phenotype?

they only have 1 allele for the gene and need 1 of each of the 2 alleles to show codominance (if the gene is not on chromosome 23 it can show codominance)

why are fruit flies used to study genetics

sexually dimorphic (males and females different) making it easy to differentiate the sexes
virgin fruit flies physically distinctive from mature adults
easy to obtain virgin flies for genetic crosses
short generation time (10-12 days)
care + culture requires little equipment

how many different genes, alleles and phenotypes are there in epistasis?

2 genes
4 alleles
3 phenotypes

how many genes , alleles and phenotypes are there in co-dominance?

1 gene
2 alleles
3 phenotypes

how many genes, alleles and phenotypes are there in a dihybrid cross?

2 genes
4 alleles
4 phenotypes

how many genes, alleles and phenotypes are there on a sex linked cross?

1 gene
2 alleles
2 phenotypes

what is the hardy weinberg allele frequency equation

p+q=1
p=frequency of dominant allele
q= frequency of recessive allele

what is the hardy weinberg genotype frequency equation

p² + 2pq + q² =1
p²=homozygous dominant
2pq=heterozygous
q² = homozygous recessive

what does the hardy weinberg principle assume

no mutations
no gene flow
large population
no selection occurring
mating is random