Monogenic inheritance Flashcards
What is monogenic inheritance?
Inheritance of a single gene.
How to perform a genetic cross?
~State phenotype of both
parents
~State genotype of both parents
—-> e.g: B = brown fur
b = white fur
~State gametes of both parents
~ Use punnet square –> label
gametes on edge of square
~State proportion of each
genotype
~ State corresponding
phenotype for each possible
genotype
What is a homozygous genetic cross?
Known as pure breeding individuals.
All offspring are heterozygous
e.g: all offspring show dominant trait
F1 generation
What is a heterozygous genetic cross?
Ratio = 3:1
Offspring produced known as F2 generation
Define codominance:
Occurs when 2 different alleles occur for a gene both which are equally dominant
Both alleles = expressed in phenotype.
e.g: snap dragon flowers
How are snap dragons codominant?
Red colour allele –> codes for production of enzyme to catalyse production of red pigment.
White colour allele –> codes for enzyme that does not catalyse pigment
Pink flower – heterozygous –> codes enough pigment to produce pink flowers
How to represent codominace cross?
Cr = red pigment
Cw = no pigment
What are the ratios for a codominance cross?
Homozygous genetic cross = 100% pink flowers
Heterozygous genetic cross = 1:2:1
Define ‘multiple alleles’:
Genes that have more than two versions but only 2 versions of gene can be expressed
e.g: blood group
Describe the process of a multiple allele cross:
Gene I ( immunoglobulin gene) codes for production of different antigens on RBC surface.
- Ia - antigen A
- Ib - antigen B
- Iº - production of neither antigen
A + B = dominant
O = recessive
- Blood group A - IAIA or IAI°
- Blood group B - IBIB or IBI°
- Blood group AB - IAIB
- Blood group O - IºI°
How is the sex of a species determined?
23rd pair = sex chromosomes
XX = females
XY = males
50% chance
Define sex linkage:
Characteristics determined by genes carried on sex chromosome.
Y chromosome = smaller –> only 1 copy compared to X chromosome.
Recessive allele on X chromosome occurs more frequently in males
–> e.g: colourblindness
What is haemophilia?
Sex-linked genetic disorder.
Blood = clots at slow pace due to absence of protein blood-clotting factor .
Lead to prolonged bleeding.
Why are males more likely to inherit haemophilia?
Cannot have corresponding dominant allele on their
Y chromosome.
Heterozygous females = carriers
How does the cross look like for haemophilia?
XH = dominant female
Xh = recessive female
(faulty allele)
Y = male
Define dihybrid cross:
Shows inheritance of 2 different characteristics caused by 2 genes –> located in different pairs of homologous chromosomes.
Each of these genes = two or more alleles
Example of a dihybrid cross:
Pea plant cross
2 different colours
(yellow/green)
2 different shapes
(round/wrinkled)
What is the ratio for a dihybrid cross?
F1 generation = all yellow round seeds
F2 generation = 9:3:3:1
