Inheritance flashcards

Topic 5: Inheritance

Sexual vs asexual reproduction

Sexual: fusion of male and female gametes; genetic information from two parents is mixed, giving variety. Asexual: one parent, no fusion of gametes, no mixing, so the offspring are genetically identical clones.

Mitosis vs meiosis

Mitosis: a body cell divides once into two genetically identical cells with the full set in pairs; for growth and replacement. Meiosis: a cell in a reproductive organ divides twice into four gametes with a single set (human 46 → 23).

Stem cells and therapeutic cloning

Stem cells from human embryos or adult bone marrow can be made to differentiate into many types of human cell, possibly to treat conditions such as paralysis. In therapeutic cloning the embryo carries the patient's genes, so the cells are not rejected.

Benign vs malignant tumours, and carcinogens

Both are abnormal, uncontrolled cell growth. Benign: does not invade healthy tissue. Malignant: invades tissue, cells may enter the blood and form secondary tumours. Carcinogens: tobacco smoke chemicals, asbestos, ionising radiation.

Sex determination, and the chance that four children are all boys

Females XX, males XY; eggs all carry X, sperm half X and half Y, so P(boy) = 1/2 every time. Four boys: (1/2)⁴ = 1/16.

Dominant, recessive and carrier

Dominant: shows in the phenotype when present on one chromosome only. Recessive: shows only when no dominant allele is present. Carrier: a heterozygous person with a recessive disorder allele who does not show the disorder.

Two heterozygous tall pea plants (Rr) give 80 seedlings. Expected numbers?

Rr × Rr gives 3 tall : 1 short. Tall: 80 × 3/4 = 60. Short: 80 × 1/4 = 20. Counts such as 57 and 23 still fit, because fertilisation is random.

How did Mendel work, and what did he find?

He used garden peas with clear either-or characteristics, began with pure-breeding lines, studied one characteristic at a time, controlled the crosses and counted large numbers. The second generation was about 3 : 1 (5474 round to 1850 wrinkled seeds).

How many bases code for a protein of 210 amino acids?

Three bases code for one amino acid, so at least 210 × 3 = 630 bases. The base sequence decides the order of amino acids.

Polydactyly, cystic fibrosis, sickle cell anaemia and Down's syndrome

Polydactyly (extra fingers or toes): dominant allele. Cystic fibrosis (thick sticky mucus) and sickle cell anaemia: recessive alleles. Down's syndrome: an extra chromosome (47 in body cells), not an allele.

Adult cell cloning in steps

Remove the nucleus from an unfertilised egg cell; insert the nucleus from an adult body cell; an electric shock makes the egg cell divide into embryo cells; place the ball of cells in the womb of an adult female. The offspring matches the body-cell donor.

Genetic engineering in steps, and concerns about GM crops

Enzymes isolate the gene; it is put into a vector (a bacterial plasmid or a virus); the vector inserts it into the cells, early in development. Concerns: effects on wild flowers and insects; uncertain effects of eating GM crops on health.