Genetic Inheritance and Sex Determination Systems

Purpose of pedigree analysis

To track inheritance of traits and identify genetic diseases in families.

Mutation rate of haemophilia

2 × 10⁻⁵.

Inheritance pattern that skips generations

Autosomal recessive.

Three autosomal recessive disorders

PKU, Albinism, Sickle-cell anaemia.

Inheritance pattern where trait appears in every generation

Autosomal dominant.

Chance of affected autosomal dominant parent passing trait

50% if heterozygous.

Two autosomal dominant traits

Huntington's disease, Polydactyly.

Who expresses X-linked traits more likely

Males, because they have only one X chromosome (hemizygous).

Inheritance of haemophilia

X-linked recessive; passed from carrier mothers to sons.

Function of the SRY gene in humans

It triggers testis development and initiates male differentiation.

Chromosome carrying the SRY gene

The Y chromosome (short arm, Yp).

Parthenogenesis

Asexual reproduction where an ovum develops without fertilization.

Difference between hermaphrodite and gonochoric organisms

Hermaphrodite: both sex organs; Gonochoric: separate sexes.

How the slipper limpet determines sex

By position in the stack; males can turn female when needed.

Organisms exhibiting temperature-dependent sex determination (TSD)

Crocodiles, some turtles, and lizards.

Enzyme involved in TSD

Aromatase; converts testosterone to estradiol.

Haplodiploidy system in bees

Males are haploid (from unfertilized eggs), females are diploid (from fertilized eggs).

Sex chromosome system in grasshoppers

XX for females, XO for males (no Y chromosome).

Sex determination system in birds

ZZ for males, ZW for females.

Difference between monoecious and dioecious plants

Monoecious: male and female flowers on the same plant; Dioecious: on separate plants.