Sex determination Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Biology — Higher

What are the typical sex chromosome combinations in human females and males?

Females: XX; males: XY.

How do the egg and sperm determine the offspring’s sex chromosome combination?

The egg contributes X; the fertilising sperm contributes X or Y, producing XX or XY, respectively.

What does a monohybrid cross predict, and how?

It predicts inheritance of one characteristic by combining the alleles each parent can pass on to find possible offspring genotypes.

How does a Punnett square show possible offspring genotypes?

Possible parental alleles are placed along the edges; each cell shows a possible offspring genotype.

How are offspring genotypes used to find a phenotypic ratio?

Use the genotypes to predict the offspring phenotypes, then calculate their ratio.

With one dominant and one recessive allele, what phenotypic ratio is predicted from crossing two heterozygous parents?

3:1 dominant to recessive.

With one dominant and one recessive allele, what phenotypic ratio is predicted from crossing a heterozygous parent with a homozygous recessive parent?

1:1 dominant to recessive.

What is the chromosome complement of an ordinary human body cell?

It is diploid, with 46 chromosomes arranged in 23 pairs.

How are the chromosomes in each human pair inherited?

One chromosome comes from each parent.

How are the 23 human chromosome pairs classified?

22 pairs are autosomes and one pair consists of sex chromosomes.

What kinds of genes do human autosomes carry?

Genes for many inherited characteristics.

What roles do human sex chromosomes have?

They typically determine chromosomal sex and also carry genes affecting other characteristics.