7.1 Inheritance Flashcards
What is a genotype?
The genes that an organism has
What is phenotype?
The observable characteristics of an organism
Comprised of the genotype and environmental factors
What is a dominant allele?
Only one allele is required for the characteristic to be expressed in the phenotype
What is a recessive allele?
The characteristic is only expressed in the absence of a dominant allele
2 alleles are required for the phenotype to be expressed
What is a co-dominant allele?
Both alleles are expressed equally and contribute to the phenotype
Either a blend or both are shown
What does pure breeding mean?
You breed a homozygous pair of alleles
What is an allele?
A version of a gene
What is homozygous and heterozygous?
Homozygous - same type of allele
Heterozygous - different types of alleles
What is the locus?
The specific position of the gene on a chromosome
What are homologous pairs?
The have the same genes but different alleles
What do we use to workout the offspring phenotypes and genotypes?
Genetic cross diagram
What is monohybrid inheritance?
A phenotype is controlled by a single
1 gene - 1 characteristic - 2 alleles
In monohybrid inheritance what are the ratios for F(0) and F1 of homozygous dominant and homozygous recessive crosses?
1
And
3:1 (this is from crossing the genotypes of the first cross)
What is dihybrid inheritance?
When two characteristics are studied and is determined by two different genes that are present on two different chromosomes at the same time
2 genes - 2 characteristics - 2 chromosomes
What gametes can you have from these two examples in dihybrid inheritance?
RRGG
RrGg
RRGG = RG
RrGg = RG Rg rG rg
What is codominance?
Both alleles in a heterozygous organism are equally dominant and are both expressed in the phenotype
2 alleles dominant
What is an example of codominance for red colour and white colour? F0
Genotypes?
Gametes?
Offspring?
Genotypes = C^RC^R and C^WC^W (C is used for colour)
Gametes = C^R C^R C^W C^W
Offspring = C^RC^W = pink 100%
What is an example of codominance for red colour and white colour? F1 (second cross)
Genotypes?
Gametes?
Offspring?
Genotypes = C^RC^W and C^RC^W (C is used for colour)
Gametes = C^R C^W C^R C^W
Offspring
C^RC^R = red 25%
C^RC^W = pink 50%
C^WC^W = white 25%
What is multiple alleles?
More than 2 alleles for 1 gene
Look for supercripts
Example of multiple alleles?
Blood groups
What do the alleles of the blood groups produce? (co-dominance example)
I referring to Gene I (immunoglobulin gene)
I^A = antigen A I^B = antigen B I^O = produces neither A or B
A and B are co-dominant
O is recessive
What are the combinations of blood groups?
Blood Group A
I^AI^A or I^AI^O
Blood Group B
I^BI^B or I^BI^O
Blood Group AB
I^AI^B
Blood Group O
I^OI^O
What is sex linkage?
The expression of an allele dependent on the gender of the individual
(As the gene is located on a sex chromosome)
Look for father-daughter relationships in pedigree charts (often on X)
What are the sex chromosomes in humans?
Male - XY
Female - XX
What is significant about sex linked traits?
Most are located on the X chromosome
Because there is no equivalent locus on the Y chromosome
(The X chromosome is double the size)
What should you be weary of with sex linkage?
That animals probably won’t be represented by X and Y sex chromosomes
What is an example of a sex linkage?
Haemophilia
Blood clots slowly can lead to slow internal bleeding
What are some genetic facts of haemophilia?
Male affected X^hY
Female affected X^hX^h
=Recessive h
Carried by the X chromosome
If a boy is born the X has to come from the mother
She can be a carrier without having it
What is an autosome?
All the non sex chromosomes
= 44 in humans
What is autosomal linkage?
Two or more genes are on the same autosomal chromosome
They are linked and stay together during independent segregation in meiosis = inherited together
In autosomal linkage if you have two homologous pairs (4 chromosomes paired) what is the result of the gametes?
They will have 4 different types of gametes
1st pair of chromosomes = AA and aa
2nd pair of chromosomes = BB and bb
= AB Ab aB ab
In autosomal linkage if you have one homologous pair (2 chromosomes paired) what is the result of the gametes?
There will be 2 different types of gamete
1st chromosome in the pair
= AA BB
2nd chromosome in the pair
= aa bb
= AB and ab
Where can autosomal linkage be different?
If crossing over takes place different gametes will form
What is significant about the closeness of loci on genes?
The more closely linked they are
What happens in Epistasis?
One gene locus affects the other gene locus
One gene loci can either mask or suppress the expression of another gene locus
2 genes leading to one characteristic (1 gene can mask the expression of the other)
What happens in recessive epistasis?
When a recessive allele prevents the expression of another allele at the second locus
Ratio - 9:3:4
What happens in dominant epistasis?
When a dominant allele at one locus completely masks the alleles at the second locus
Ratio - 12:3:1
