Pack 12 Flashcards
Define the genotype of an organism.
All the alleles that an organism has.
What does the genotype of an organism determine?
The limits within which the characteristics of an individual.
Other than the genotype of an organism what else can effect characteristics of an individual?
The environment - e.g. diet
Define phenotype. What is it the result of?
- The observable or biochemical characteristics of an organism.
- Result of the interaction between the expression of the genotype and the environment.
What is a gene what does it code for?
A length of DNA nucleotide bases. Usually codes for a polypeptide.
What is the name for the different forms of genes?
alleles
What is the position of a gene on a particular DNA molecule known as?
Locus
How many alleles can occur at the locus of any one chromosome?
1
How many gene loci are there for each gene in diploid organisms? Therefore how many alleles can each organism have of each gene?
2 - 2
What is the organism the allele on each chromosome is the same?
Homozygous
What is the organism the allele on each chromosome is the different?
Heterozygous
What is the allele of the heterozygote that expresses itself in the phenotype called?
Dominant
What is the allele of the heterozygote that does not express itself in the phenotype called?
Recessive
What is a homozygous organism with two dominant alleles called?
Homozygous dominant
What is a homozygous organism with two recessive alleles called?
Homozygous recessive
When Is the effect of a recessive allele apparent in the phenotype of a diploid organism?
When it occurs in the presence of another identical allele - homozygous recessive.
What are codominant alleles?
Two alleles both are expressed in the phenotype when they are different.
What is the organism referred to when a gene has more than two allelic forms.
Has multiple alleles for that character.
When representing a character why do you use uppercase for dominant and lower case for recessive and not two different letters?
Two different letters implies codominance.
What should you write when showing a cross before drawing a punnet square? (3)
The parents genotypes and phenotypes. Draw the gametes produced.
When a pure bred green (GG) plant is crossed with a pure bred yellow (gg) what are the offspring called? What is their genotype and phenotype?
First filial generation F1 generation. Gg - Green
When the F1 generation is crossed? What are the offspring called and what ratio are they in?
F2 generation. Green:yellow - 3:1
How many alleles of each gene can be present in a single gamete?
1
How should a ratio be written in biology?
X:1
Why are Mendel’s results not exactly 3:1 in the F2 generation?
Statistical error - chance.
What makes the results of a genetic cross experiment more representative?
Larger sample size.
What is dihybrid inheritance?
How two characters determined by two different genes located on different chromosomes are inherited.
For dihybrid inheritance where must the two genes be located.
On two different chromosomes.
R=Round seeds r = wrinkled seeds
G=yellow g=green
Consider the cross of a pure bred round yellow seed plant and a wrinkled green seed plant.
What are the parental genotypes?
What gametes are produced by each plant?
- RRGG; rrgg
- RG; rg
R=Round seeds r = wrinkled seeds
G=yellow g=green
Consider the cross of a pure bred round yellow seed plant and a wrinkled green seed plant.
What are the phenotypes and genotypes of the F1 generation?
RrGg - Round Yellow
R=Round seeds r = wrinkled seeds
G=yellow g=green
Consider the cross of a pure bred round yellow seed plant and a wrinkled green seed plant.
What gametes does the F1 generation produce?
RG, Rg, rG, rg
R=Round seeds r = wrinkled seeds
G=yellow g=green
Consider the cross of a pure bred round yellow seed plant and a wrinkled green seed plant.
Give the ratio of the phenotypes produced.
Round wrinkled: round green: wrinkled yellow: wrinkled green.
9:3:3:1
What is the law of independent assortment?
Each member of a pari of alleles may combine randomly with either of another pair.
How are codominant alleles written. Example coat colour for cows Red and white colours.
C^W/C^R - superscript
In cows alleles for red and white coat pigment are codominant. If a cow has both alleles the coat is roan.
What is the genotype and phenotype of:
a) a cross between two roan cows
b) a cross between a red and a white cow
a) - RR:RW:WW - Red:Roan:White
- 1:2:1
b) RW - roan
In cows alleles for red and white coat pigment are codominant. If a cow has both alleles the coat is roan.
What colour coat does a heterozygous individual have?
Roan
The gene I for immunoglobulin (ABO blood type) has three alleles. What is this called?
Multiple alleles.
What are the three alleles for ABO blood type? Which are dominant to which?
A, B, O (Should be I superscript)
A and B are codominant, O is recessive.
What are the ratios of phenotypes and genotypes of a cross between someone blood group O and AB?
AO (A): BO (B)
1:1
What are the ratios of phenotypes and genotypes of a cross between someone blood group A (AO- heterozygous) and group B (BO - heterozygous)?
AB: BO (B): AO (A): OO (O)
1:1:1:1
In what way are all females gametes the same? And in what way are males gametes different.
All female gametes contain the X chromosome. Half of male gametes contain an X chromosomes and the other half contain the Y chromosome.
What is any gene carried on either the X or Y chromosome known as?
Sex linked.
What is different about the X and Y chromosomes compared to the 22 other homologous pairs?
The X chromosome is much linger than the Y chromosome.
What is the result of the fact that the Y chromosome is shorter than the X in terms of the expression of alleles?
For much of the length of the X chromosome there is no equivalent homologous portion on the Y chromosome.
Characteristics controlled by recessive alleles on this non-homologous portion of the X chromosome, therefore, will appear more frequently in males.
What is an X linked genetic disorder?
A disorder caused by a defective gene on the X chromosome.
H = allele for blood clotting h = defective
Give the ratio of phenotypes and genotypes of the cross between a carrier female (Hh) and a normal male (X^H Y).
Females - HH:Hh - normal:carrier - 1:1
Males - H:h - normal:haemophiliac - 1:1
*X superscript should be used
Why do males always inherit haemophilia from their mother?
The defective gene is carried on the X chromosomes. Males inherit their X chromosome from their mother and their Y from their father.
What is the genotype of a female ‘carrier’ of haemophilia?
X^H X^h
What are two genes that occur on the same chromosomes called?
Linked
What is an autosome?
A chromosome that is not a sex chromosome.
Define autosomal linkage?
Two or more genes are carried on the same autosome.
Assuming no crossing over, why is autosomal linkage significant in terms of inheritance?
All the linked genes remain together during meiosis and so pass into gametes together.
If two genes are linked in a heterozygous individual (both dominant alleles are on the same homologous pair) what are the possible gametes produced? use A and B
AB or ab
Two autosomal linked genes are:
G/g and N/n
Two individuals that are heterozygous for both (dominant allele on the same chromosomes) are crossed.
Assuming no crossing over give the offspring genotypes and the ratio of the phenotypes.
GGNN, 2x GgNn, ggnn
3:1 - dominant for both:recessive for both
Explain why the actual ratio of offspring of two autosomal linked genes may not be 3:1?
Crossing over.
Explain why the actual ratio of offspring after a genetic experiment may not be the same as the expected ratio. (3)
Small sample size; fertilisation of gametes is random; offspring ratios are a probability not fixed - arise by chance.
Define epistasis.
Where the allele of one gene affects or masks the expression of another.
In mice gene A controls distribution of black pigment.
A- produces agouti aa produces black.
Gene B: B- leads to the production of melanin.
bb leads to on pigment (albino).
Give the ratio o phenotypes and genotypes of a cross between two agouti mice (AaBb)
Explain the results.
AABB AABb AaBB AaBb
AaBb Aabb AaBb Aabb
AaBb AbBb aaBB aaBb
AaBb Aabb aaBb aabb
9:4:3 agouti to white to black
Same as dihybrid except the “1” or the “albino and black” is just albino because it masks the black allele.
