Alleles and sex determination

What are alleles?

Alleles are different versions of the same gene. They can be dominant or recessive, influencing how traits are expressed.

What is the difference between a dominant and a recessive allele?

• Dominant allele: Always expressed if present (e.g., Bb).

• Recessive allele: Only expressed if two copies are present (e.g., bb).

What do genotype and phenotype mean?

• Genotype: The combination of alleles an organism has

• Phenotype: The physical expression of the trait (e.g., brown or blue eyes).

What do homozygous and heterozygous mean?

• Homozygous: Two identical alleles ( BB or bb)

• Heterozygous: Two different alleles ( Bb)

What are sex chromosomes, and how do they determine sex?

• Females have two X chromosomes (XX).

• Males have one X and one Y chromosome (XY).

• The Y chromosome carries a gene that triggers male development.

How is biological sex determined in offspring?

• The egg always carries an X chromosome.

• The sperm carries either an X or a Y.

• If the sperm carries X → Female (XX).

• If the sperm carries Y → Male (XY).

There is a 50% chance of having a boy or a girl.

What does a Punnett square for sex determination look like?

Ratio: 1 : 1 (50% chance of male or female)

Why are some genetic disorders more common in males?

• Genes on the X chromosome affect males more because they only have one X.

• Males (XY) only have one X, so if they inherit a faulty allele, they have no second copy to compensate.

• Example: Color blindness and haemophilia are more common in males.

why isn’t sex deterimination monohybrid inheritance

a pair of genes controls sex not a single gene

other than genetics what is another factor in genetic inheritance

environment

what is polygenic inheritance

characteristics that are as a result of multiple genes interacting