Flashcards · 0610 · Topic 17

Inheritance flashcards

24 cards on Topic 17, subtopics 17.1 to 17.4. Pick a subtopic or study them all.

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17.1 Chromosomes, genes and proteins

Gene: A length of DNA that codes for a protein. (Chromosomes are made of DNA.)
Gene vs allele: The gene is the length of DNA for a feature; alleles are its alternative forms.
Inheritance of sex in humans: Females are XX, males XY. All eggs carry X; half of sperm carry X and half Y. The chance of a boy is 1/2 at every birth.
How a gene controls a proteinExtended: The sequence of bases in the gene sets the sequence of amino acids, which sets the shape of the protein and therefore its function (e.g. enzymes, membrane carriers, receptors for neurotransmitters).
Outline of protein synthesisExtended: The gene stays in the nucleus; an mRNA copy is made there and moves to the cytoplasm; it passes through a ribosome, which joins amino acids in the order set by the mRNA base sequence.
Haploid vs diploid nucleusExtended: Haploid: a single set of chromosomes (human gamete: 23). Diploid: two sets (human body cell: 23 pairs, 46).
Why does a muscle cell not make insulin although it has the insulin gene?Extended: Most genes in a cell are not expressed: each cell makes only the proteins it needs.

17.2 Mitosis

MitosisExtended: Nuclear division giving rise to genetically identical cells.
Roles of mitosisExtended: Growth, repair of damaged tissues, replacement of cells, and asexual reproduction.
What happens to chromosomes before and during mitosis?Extended: Before: exact replication of the chromosomes. During: the copies of the chromosomes separate, so the chromosome number is maintained.
Stem cellExtended: An unspecialised cell that divides by mitosis to produce daughter cells that can become specialised.

17.3 Meiosis

MeiosisExtended: A reduction division in which the chromosome number is halved from diploid to haploid, giving genetically different cells.
Role of meiosisExtended: Production of gametes.
Mitosis vs meiosisExtended: Identical and same number vs different and halved.
A dog body cell has 78 chromosomes. How many in a dog sperm and a dog zygote?Extended: Sperm (made by meiosis, haploid): 39. Zygote (diploid): 78.

17.4 Monohybrid inheritance

Genotype vs phenotype: Genotype: the genetic make-up of an organism in terms of the alleles present. Phenotype: the observable features of an organism.
Homozygous vs heterozygous; pure-breeding: Homozygous: two identical alleles of a gene. Heterozygous: two different alleles. Two identical homozygous individuals bred together are pure-breeding; a heterozygote is not.
Dominant and recessive alleles: Dominant: expressed if it is present in the genotype. Recessive: only expressed when there is no dominant allele of the gene present.
Offspring ratios of Aa × Aa and Aa × aa: Aa × Aa: 1 AA : 2 Aa : 1 aa, a 3 : 1 phenotype ratio. Aa × aa: 1 Aa : 1 aa, a 1 : 1 ratio.
Ratio v probability: 3 : 1 means a 1/4 (25%) chance of the recessive phenotype, not 1/3.
How does a pedigree show that a feature is recessive?: Two unaffected parents have an affected child. Both parents must be heterozygous, and the affected child is homozygous recessive.
Test crossExtended: Cross the dominant-phenotype organism with a homozygous recessive. All offspring dominant: it was probably homozygous dominant. Any recessive offspring: it was heterozygous.
ABO blood group alleles and genotypesExtended: Iᴬ and Iᴮ are codominant; both are dominant to Iᵒ. Group A: IᴬIᴬ or IᴬIᵒ. Group B: IᴮIᴮ or IᴮIᵒ. Group AB: IᴬIᴮ. Group O: IᵒIᵒ.
Why is red-green colour blindness more common in males?Extended: It is sex-linked: the gene is on the X chromosome, with no allele on the Y. A male (XᵇY) with one recessive allele always shows it; a female needs two (XᵇXᵇ).