paper 2: Inheritance and Populations Flashcards
define gene
a base sequence of DNA on a chromosome which codes for the amino acid sequence of a polypeptide or functional RNA
define allele
a different version of a gene
define genotype
genetic constitution of an organism
define phenotype
the expression of this genetic constitution and its interaction with the environment
define a homologous chromosome
pair of chromosomes with same gene in same gene loci but can have different alleles
define homozygous dominant
homozygous organism with 2 dominant alleles
define homozygous recessive
a homozygous organism with 2 recessive alleles
define heterozygoous
the allele on each homologous chromosome is different
what does a gene being expressed mean
how it is transcribed into mRNA and then how mRNA is translated into a protein
what is meant by a dominant allele
allele is always expressed in the phenotype
what is meant by a recessive allele
allele that is only expressed in phenotype when in presence of another identical allele
define monohybrid inheritance
the inheritance of a single gene on an autosome
why are the actual results of genetic crosses rarely the same as predicted results
- random fertilisation of gametes
- may be small population
- some alleles may give selective advantage
define dihybrid inheritance
the inheritance of 2 different genes on different chromosomes at the same time
draw dihybrid genetic cross diagram of 2 heterozygous parents
what is the rule for dihybrid crosses
always produce 9:3:3:1 phenotypic ratio
define co-dominant alleles
both alleles are expressed in the phenotypes
draw out the first 2 geenrations of phenotypes produces when pure breed red (C^RC^R) and white (C^WC^W) snapdragons are bread together
define multiple alleles
more than 2 alleles in a population
define sex-linkage
a gene carried on the X chromosome
explain which sex is more likely to express the recessive alleles found on the sex chromsomes in their phenotype
males
- they only have one copy of X chromsome so only need one copy of recessive alele in genotype to express recessive phenotype wherease females have 2 X chromosomes so need 2 copies of recessieve allele in their genotype to express the recessive phenotype
find phenotype ratios
define autosomal linkage
inheritance of 2 or more genes carried on the same autosome
find phenotypic ratios for this example
define epistasis
the allele of one gene affects or masks the expression of another gene
In humans, Huntington’s disease is caused by a dominant mutant allele of a gene. Draw a genetic diagram to show the possible genotypesand phenotypes of the offspring produced between a man with one allele for the disease and woman who does not suffer from the disease.
In cocker spaniels, black coat colour is the result of a dominant allele and red coat colour is the result of a corresponding recessive allele.
Draw a genetic diagram to show a cross between a pure-breeding (homozygous) bitch with a black coat and a pure-breeding (homozygous) dog with a red coat.
In cocker spaniels, black coat colour is the result of a dominant allele and red coat colour is the result of a corresponding recessive allele.
If the offspring of this first cross are interbred, calculate the probabilitythat any one of the offspring will have a red coat. Use a genetic diagram to show your working
how do you calculate alle frequency using Hardy Weinberg
p + q = 1
p= dominant allels
q= recessive alleles
how do you calculate the genotype frequency using Hardy Weinberg
p^2 + 2pq + q^2 = 1
p^2 = homozygous dominant
2pq = heterozygous
q^2 = homozygous recessive
what are assumptions made by hardy weinberg
- mating is random
- no immigration so new new alleles indroduced
- no mutations so no new alleles created
- no selection so no alleles favoured or eliminated
- large population
