Human Genome

Biology Ch 14

Chromosomes

Karyotype – picture of all chromosomes grouped in pairs

Carries genetic information from parents to offspring

Autosomes – chromosomes paired together by size, shape, content (22 pairs)

Sex Chromosomes – one pair of chromosomes that determine gender (one pair)

Sex Chromosomes

XX = Female

XY = Male

PedigreeCan use genetic information to develop a pedigree – a chart that shows traits as passed from generation to generation

P = Parent generation

F1 = First offspring generation

F2 = next generation offspring

Pedigree Problem

Imagine that you are a genetic counselor. The pedigree shown on the next slide illustrates the inheritance of albinism in three generations of a family. A couple from the family have come to you to ask for advice about how the trait is inherited. *Your task is to determine whether the allele for albinism is dominant or recessive.*

Pedigree Problem

1. By remembering the previous slide, restate the problem that must be solved.

2. Copy this pedigree on to the paper. Label each person on the pedigree with his or her phenotype: normal (N) or albino (A).

3. Write down HOW you would analyze the pattern of inheritance of the albinism trait and describe how you will use your analysis to infer the genotype of as many individuals as possible.

Answer on a separate piece of paper:

Trait Control

Most human traits are NOT controlled by a single gene

Other controls:• Multiple genes – polygenic

• Environmental influence

Single gene trait

Multiple ControlsBlood type = CoDominance & Multiple Alleles

Alleles = IA, IB, I

IA and IB are Co-dominant AND are BOTH dominant over the recessive i

Genotype(s) IAIA , IA i IBIB, IBi IAIB ii

Polygenic trait distribution

Single gene trait distribution graph:

Autosomal Dominant Genetic Disorders: These disorders are caused when an individual has inherited the defective allele from a single parent. Ex: Aa or AA (Dwarfism, Huntington disease)Autosomal Recessive Genetic Disorders: Such disorders manifest only when an individual has got two defective alleles of the same gene, one from each parent. Ex: aa (Albinism, Cvstic fibrosis)Co-dominant alleles: Disorder manifested when two dominant alleles are inherited. Ex: AB (Sickle cell disease)Multi-factorial Genetic Disorders: Such disorders are the result of genetic as well as environmental factors. (Alzheimer’s disease?, dementia?)

Autosomal Chromosome disorders

Mutations found ONLY on the autosomes (chromosomes 1 through 22)Can be single gene mutation or polygenic mutation)

Sex linked genes Genes found X or Y chromosomes

X chromosome has approx 1000 genes – Many life functions

Y chromosome have approx 150 genes – SRY region determines male characteristics

Sex-linked traits:• Colorblindness•Hemophilia•Duchenne Muscular Dystrophy

Autosome Chromosome Disorders

Non-disjunction – results in abnormal number of chromosomes in gametes (Down Syndrome)

Sex Chromosome Disorders