Genetics Pedigrees and Karyotypes

Karyotype

What to look for in a karyotype? When analyzing a human karyotype, scientists first look for these main features: Are there 46 chromosomes? Are there 2 identical pairs of each autosome and 2 sex chromosomes? Are there any rearrangements between chromosomes or large deletions?

Chromosomes Humans have 46 chromosomes 44 chromosomes are autosomes 2 are sex chromosome Females have two X chromosomes Males one X chromosome one small Y chromosome

Pedigrees

Human pedigrees Before we consider human inheritance we need to learn the symbols used to draw pedigrees. The figure below shows some of the commoner symbols:

Pedigrees

Inheritance of sex chromosomes Egg cells contain one X chromosome Sperm cells contain either one X chromosome or one Y chromosome So in a human population, half are male and half are female

Sex linked Genes Genes located on the sex chromosomes are called sex-linked genes. Males have just one X chromosome, so all X-linked alleles are expressed in Males

Sex linked Genes Genes located on the sex chromosomes are called sex-linked genes. Males have just one X chromosome, so all X-linked alleles are expressed in Males

Sex linked Genes What percent of offspring will be girls? What percent of offspring will be boys? What percent of offspring will have normal vision? What percent of offspring will be colorblind? What percent of offspring will be carriers?

Hemophilia Pedigree

Human Pedigree.

Chromosomal Disorders Nondisjunction

Chromosomal Disorders Down syndrome –Trisomy 21 –Due to non-disjunction in second stage of meiosis

Chromosomal Disorders Sex Chromosome disorders –Turner’s syndrome Karyotype is (45,X) Only one X chromosome

Chromosomal Disorders Sex Chromosome disorders –Klinefelter’s syndrome Karyotype 47 XXY Extra X chromosome