M6, C20 Patterns of Inheritance and Variation Flashcards
define genotype
genetic make-up of an organism
define phenotype
observable characteristics of an organism
define dominant allele
version of the gene that will always be expressed if present
define recessive allele
version of a gene that will only be expressed if 2 copies of this allele are present in the organism
define homozygous
2 identical alleles for a characteristic
define heterozygous
2 different alleles for a characteristic
Describe continuous variation
give an example
continuous variation - individuals in a population vary within a range - there are no distinct categories
eg. height
describe discontinuous variation
give an example
discontinuous variation - when there are to or more distinct categories - each individual falls into only one of these categories
eg. blood group
define codominant
alleles that are both expressed in the phenotype - neither one is recessive
define locus
the fixed position of a gene on a chromosome
what are punnett squares used for
show a genetic diagram
predict genotypes and phenotypes of offspring
define sex linkage
genes when its locus is one of the sex chromosomes, X or Y
determine the possible genotypes of an offspring whose mother is a carrier of haemophilia but the father is unaffected
N is normal
n is faulty
carrier mother’s genotypes: X^N and X^n
unaffected father’s genotypes: X^N and Y
from punnett square the results show the 4 possibilities as: X^NX^N - 25% unaffected female X^NY - 25% unaffected male X^nX^N - carrier female X^nY - affected male
what are the chromosomes of females and males in mammals
what does this mean about inheritance of diseases which are transmitted to offspring during sex linkage
females - 2 X chromosomes
males - 1 X chromosome, 1 Y chromosome
the Y chromosome is smaller than the X chromosome and carries fewer genes. so most genes on the sex chromosomes are only carried on the X chromosome.
this means males often have one allele for sex-linked genes meaning they express the characteristic even if it’s recessive. they can’t be a carrier
determine the possible genotypes for a cow offspring whose parents have genotypes RR and WW
R is red
W is white
what is this an example of?
punnett square shows the possible gneotypes are:
RW, RW, RW, RW
100% red/white cow
example of codominance
define monohybrid inheritance
inheritance of a single characteristic controlled by different alleles
define dihybrid inheritance
inheritance of 2 different characteristics caused by 2 genes
what would you get if you cross two organisms each with 2 homozygous alleles
the offspring would be heterozygous for both alleles
One parent has the genotype of NNGG and the other has the genotype of nngg.
what would the genotype be for the F1 offspring
F1 offspring means first generation
two homozygous parents makes a heterozygous offspring so
NnGg
When you cross two heterozygous individuals what ratio would you expect to find for the phenotypes of the offspring
four possible phenotypes
9:3:3:1
If you cross a heterozygous organism and a homozygous recessive organism, what ratio would you expect for the phenotypes of the offspring
four possible phenotypes
1:1:1:1
two alleles show complete dominance and are located on separate chromosomes
In pea plants the dominant allele for seed shape is round shown by R and the dominant allele for seed colour is green shown by G.
The recessive alleles are r for wrinkled and g for yellow.
A round, yellow seed is crossed with a green, wrinkled seed.
Produce a full genetic cross diagram to show the ratio of 2nd generation offspring.
Two homozygous parents make a heterozygous offspring
So 1st generation offspring = RrGg
On each side of genetic cross diagram there should be the gametes of RG, Rg, rG and rg
You get 16 results of:
RRGG, RRGg, RrGG, RrGg, RRGg, RRgg, RrGg, Rrgg, RrGG, RrGg, rrGG, rrGg, RrGg, Grgg, rrGg, rrgg
Looking at the dominant and recessive alleles, this makes the ratio of 9:3:3:1 of the phenotypes: 9 round and yellow pea plants 3 round and green 3 wrinkled and yellow 1 wrinkled and green
How would you split a parent with the genotypes RrHh into gametes
R with H
R with h
r with H
r with h
SO: RH, Rh, rH and rh
(the alleles come in pairs so Rr and Hh CAN’T go together)
define autosomal linkage
when the genes that are linked are found on one of the other pair of chromosomes
how do recombinants form
hint: meiosis
- When the chromosomes pair up in prophase 1 of meiosis, crossing over occurs between the non sister chromatids, resulting in an exchange of the genes
- Some of the linked genes are separated
- They will have a different combination than either of the parents, so are called recombinants
- The closer the genes are on the chromosome, the less likely they are to separate
what is recombination frequency
the measure of the amount of crossing over in meiosis
what is the equation for recombination frequency
what do the results show
number of recombinant offspring / total number of offspring
50% or more = no linkage (genes are on separate chromosomes)
Less than 50% = there is gene linkage (random process of independent assortment has been hindered)
what is the chi-squared test
tests whether the difference between the observed and expected results are due to chance or whether there is a significant difference and so your experiment or prediction you made must be wrong
χ^2 = Σ(O-E)^2 / E
This is the chi-squared formula. What do all the parts stand for?
χ^2 = chi-squared O = observed results E = expected results