Unit 7a - Inheritance Flashcards
What is the meaning of the words “genotype” and “phenotype”?
Genotype - the genetic constitution of an organism
Phenotype - observable characteristics of an organism
Why do human phenotypes not always closely match their genotypes?
Some of our genes in our phenotypes are not expressed
Define:
Gene
Allele
Locus
Chromosome
Gene - a series of nucleotide bases that codes for a polypeptide
Allele - two or more variations of a gene
Locus - position of a gene on a chromosome
Chromosome - thread-like structures that contains genetic information
In meiosis, how is variation achieved within the gametes produced by a parent?
Independent segregation and crossing over
Explain the value of variation within gametes
The fertilisation of gametes during meiosis are random
A father with genotype Hh and a mother with genotype hh have children. H = Huntington’s Disease and h = healthy. Draw a genetic cross diagram to show the different possible offspring. Label the phenotypes of offspring and the probability of each offspring type being born?
Hh = carrier
hh = healthy
50/50 or 1:1 ratio
Why are the results of genetic crosses rarely a match for the statistical ratio?
There may be mutations that could occur during meiosis
Draw a 16-box diagram to show the outcome of a genetic cross between two Labrador dogs; both parent dogs have the following genotype:
BbHh
…and where each allele codes as follows:
• B - black fur colour
• b - golden fur colour
• H - short hair
• h - long hair
And identify all phenotypes in the offspring using a key.
B-H- (9x) = black fur colour; short hair
B-h- (3x) = black fur colour; long hair
b-H- (3x) = golden fur colour; short hair
b-h- (1x) = golden fur colour long hair
What are the normal ratios expected in genetic crosses between animals with a:
• Monohybrid heterozygous cross
• Dihybrid heterozygous cross
Monohybrid cross = 3:1
Dihybrid cross = 9:3:3:1
In the event that offspring phenotypes do not match these ratios, what could be the explanation?
Mutation occurred during meiosis
Draw a genetic cross diagram to show the blood type phenotypes within human offspring that were born of a union between two parents with the following genotypes:
• Father - |B |A
• Mother - |B |A
|B |B
|A |B
|A |B
|A |A
Which chromosomes code for male and female sex in humans?
Female - XX chromosome
Male - XY chromosome
What are the other 22 chromosome pairs called?
Autosomes
Draw a genetic cross diagram to predict the likelihood of having a child suffering from Duchenne Muscular Dystrophy with parents carrying the following alleles:
• Mother - Xd XD
• Father - XD Y
where Xd is the allele responsible for causing Muscular Dystrophy.
It is less likely to have a child suffering from Duchenne Muscular Dystrophy (Xd) - 25% chance
Explain why sex-linked diseases affect male babies far more frequently than females
Male babies only have one X chromosome whereas female babies have two X chromosomes
Explain how a female haemophiliac child could be born
When the mother is a carrier and the father is haemophiliac, there is 25% chance that a female haemophiliac could be born
Explain why there are very few females with colour blindness; explain why there are very few female haemophiliacs
Females have two X chromosomes so females with colour blindness and haemophiliacs is less likely to occur
What does it mean if two genes have autosomal linkage
Fewer genetic combinations of alleles are possible therefore reducing the variation in offspring
In cats, the genes for tooth length and claw colour are autosomally linked, with the following alleles:
• T - long teeth
• t - dwarf teeth
• C - beige claws
• c - brown claws
With two parent cats that both have the allele combinations TtCc, state the gametes that they would produce. Draw a genetic cross diagram to show the possible offspring. Label the phenotypes
Gametes that they would produce - male/female
T-C- (9x) = long teeth; beige claws
T-c- (3x) = long teeth; brown claws
t-C- (3x) = dwarf teeth; beige claws
t-c- (1x) = dwarf teeth; brown claws
What is epistasis?
When one gene modifies or masks the expression of a different gene at a different locus
In mice, the following genes are responsible for fur colour and colour uniformity:
A - hairs with black bands
a - hairs with a uniform colour
B - melanin (pigment)
b - no melanin
Generate gametes for two mice, one of which has the genotype AABb and the other AaBb, using a 16-box diagram and identify the phenotypes.
What is the purpose of the X2 test?
To determine the differences between two datas
