4.3 Define…

Mendel’s experiments

Mendel’s experiments

Monohybrid cross: A cross that tracks the inheritance of a single character.

25%white-flower peas

F2

75%purple-flower peas

3:1

true-breedingpurple-flower peas

true-breeding white-flower peas

P

100%F1

self-pollinate

Flower colour Mendel’s experiment:

Therefore, the Principle of Segregation indeed is a general principle of genetics.

Mendel’s experiments

Mendel’s conclusions:1. Inheritance is not blended.

2. The inheritable factor for white color was not lost, it was masked by the presence of

purple color factor.

3. The hybrid plants inherit one factor from each parent and so have two different factors.

4. When they form male and female gametes they pass on either the dominant or the

recessive factor, not both.

Mendel’s Law of Segregation:

Each genetic trait is produced by a pair of

alleles which separate during reproduction.

During meiosis, each gamete only gets one

copy of the genetic trait.

Mendel’s conclusions:Mendel’s Law of Segregation:

4.3.2 Punnet Squares

(1) Define symbols:

P = Purple allele

p = White allele

(2) State the cross

(3) Diagram the gametes

(4) Complete the squares

(5) Summarize the results:

Genotype

Phenotype

In a Punnett square for a monohybrid cross, the Principle of Segregation is applied.

How can you determine genotype from individual expressing dominant

phenotype? - DD or Dd?

Cross the individual with dominant

phenotype with a homozygous

recessive individual.

Monohybrid test cross

4.3.2 Punnet Squares

Others inheritance pattern

Multiple alleles: ABO group

Co-dominance

4.3.5 Determination of gender in humans

How many chromosomes do humans have?

How many pairs of chromosomes?

How many of them are autosomes?

How many of them are sex chromosomes ?

4.3.5 Determination of gender in humans

Some genes are present on the

X chromosome and absent from

the shorter Y chromosome in

humans

4.3.7 Define sex linkage

Genes located on a sex chromosome are called sex linked genes.

In humans the term usually refers to X-linked characters: genes located only

on X chromosomes.

Fathers can pass X-linked alleles to their daughters, but not sons.

Mothers can pass sex-linked alleles to both sons and daughters.

♀:2 X’s ChromosomesHomozygous or Heterozygous

for a sex-linked trait

♂:1 X ChromosomeHemizygous

for a sex-linked trait

Shows a recessive trait even with only one

recessive allele

4.3.8 Describe the inheritance of colour blindnessThe allele of color vision is carried on the part of the X chromosome that is missing from

the Y chromosome. This means that a male will only have one allele for color vision.

There is a defective, recessive allele of the color vision gene which can lead to color

blindness, particularly of red and green light.

C= allele for normal vision

c= allele for color blindness

4.3.8 Describe the inheritance of colour blindness

What happens if we cross a normal sighted female with

a color blind male?

What happens if we cross a normal sighted male with

a carrier female?

4.3.8 Describe the inheritance of Haemophilia

Haemophilia is a sex-linked disease, caused by a recessive allele on the X chromosome.

The gene that codes for Factor VIII, an important protein involved in blood clotting, is a

sex-linked gene found on the X chromosome.

A defective recessive allele of the gene can lead to haemophilia.

H= normal allele

h= haemophiliac allele

 Females can be homozygous or heterozygous for the sex-linked alleles

4.3.9 Female and sex linkage

 4.3.10 Females carriers for X-linked recessive alleles.

•Carrier are individuals that are heterozygous for the allele.

•The have both the dominant and the recessive (disease) allele.

•Carriers do not have the disease.

 4.3.11 Predict genotypic and phenotypic ratios…

Pedigree Charts: Pedigree charts show a record of the family of an individual They can be used to study the transmission of a hereditary condition They are particularly useful when there are large families and a good family

record over several generations.

Generations are identified by Roman numerals

Individuals in each generation are identified by Arabic numerals numbered

from the left

Therefore the affected individuals are II3, IV2 and IV3

I

II

III

IV

Pedigree Charts:

Females who have more than four sons, with none exhibiting hemophilia, are likely to have the

genotype NN. If she has had four or fewer sons her genotype is less certain. In such cases her

genotype is labeled N_. LABEL THE REST OF THE FEMALES AS EITHER N? OR NN.

Q10 What is the probability of parents 1 and 2 having a hemophiliac child ?

Q11 Is there any chance of parents 3 and 4 having a hemophiliac son ? Explain.

Figure I Hemophilia Pedigree

 4.3.11 Deduce the genotypes and phenotypes …

 4.3.11 Predict genotypic and phenotypic ratios…