Mitosis & Meiosis
What is the main purpose of mitosis?
Growth, repair and replacement of cells.
What is heredity?
The passing of genetic information or traits from parents to offspring.
What does DNA stand for?
Deoxyribonucleic acid.
What does a capital letter represent in a Punnett square?
A dominant allele.
What does a square represent on a pedigree?
A male.
How many daughter cells are produced by meiosis?
Four.
What is the difference between a genotype and a phenotype?
Genotype is an organism's allele combination; phenotype is the observable characteristic.
How many chromosomes are normally found in a human body cell?
46 chromosomes, or 23 pairs.
If B = brown eyes and b = blue eyes, what phenotype would Bb have?
Brown eyes.
What does a shaded symbol usually represent on a pedigree?
An individual who has the trait being studied.
Give two differences between mitosis and meiosis.
Mitosis produces 2 identical diploid cells; meiosis produces 4 genetically different haploid cells.
What is the difference between a dominant and recessive allele?
A dominant allele can be expressed with one copy, while a recessive allele generally requires two copies to be expressed.
Explain the relationship between DNA, genes and chromosomes.
DNA is genetic material. Genes are sections of DNA, and DNA is packaged into chromosomes.
Cross Bb × bb. What percentage of offspring are expected to show the recessive phenotype?
50%.
Two unaffected parents have an affected child. Is the affected trait most likely dominant or recessive?
Recessive.
Why does meiosis produce genetically different cells, while mitosis normally produces genetically identical cells?
Meiosis includes processes such as crossing over and independent assortment that create genetic variation. Mitosis produces genetically identical cells.
A person has one dominant allele and one recessive allele. What term describes their genotype?
Heterozygous.
Why do human gametes contain 23 chromosomes rather than 46?
Gametes are haploid so that when sperm and egg combine, the offspring has the normal 46 chromosomes.
In the cross Tt × Tt, what are the expected genotype and phenotype ratios?
Genotype = 1 TT : 2 Tt : 1 tt. Phenotype = 3 dominant : 1 recessive.
How can a pedigree indicate that an unaffected person is heterozygous for a recessive trait?
If they have an affected child, they must carry the recessive allele.
A human cell containing 46 chromosomes undergoes meiosis. How many cells are produced, how many chromosomes does each contain, and why is this important?
4 cells are produced, each with 23 chromosomes. This allows fertilisation to restore the normal 46 chromosomes.
Two parents do not show a recessive genetic condition, but their child does. Explain how this is possible.
Both parents can be heterozygous carriers. The child can inherit one recessive allele from each parent and therefore have the condition.
What are homologous chromosomes, and where does one chromosome in each pair come from?
Homologous chromosomes are matching chromosome pairs that contain genes for the same traits. One chromosome comes from the mother and one from the father.
A recessive genetic condition has two carrier parents. What is the probability their child is affected, a carrier, or unaffected and not a carrier?
25% affected, 50% carrier, 25% unaffected non-carrier.
In a pedigree, two parents are both unaffected but have an affected child. What does this tell you about the parents if the trait is recessive?
Both parents must be carriers (heterozygous) for the recessive allele.