Inheritance Patterns and Human Genetics Chapter 12: Inheritance Patterns and Human Genetics

Chromosomes and Inheritance KEY CONCEPT Chromosomes are the mode of genetic inheritance in humans

Two Types of Human Chromosomes Sex Chromosomes – contain genes that determine the gender (sex) of an individual

Two Types of Human Chromosomes Autosomes – all other chromosomes which are not directly involved in gender determination

Gender (Sex) Determination Read the first paragraph under the heading ‘Sex Determination’ on page 236. SRY – Sex-determining Region Y: is a gene on the Y-chromosome that codes for a protein that causes the gonads of and embryo to develop as testes.

Sex-linked Trait – a trait coded by an allele on a sex chromosome Sex-Linked Genes and Traits Sex-linked Trait – a trait coded by an allele on a sex chromosome Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will exhibit the sex-linked trait.

The X-chromosome is much larger than the Y-chromosome Sex-Linked Genes and Traits The X-chromosome is much larger than the Y-chromosome This causes there to be many more X-linked than Y-linked traits

Linked Genes Linked Genes – pairs of genes that tend to be inherited together because they are close to each other on a chromosome Because they are close to each other, they are less likely to be separated in crossing over during meiosis

Chromosome Mapping Chromosome Map – a diagram that shows the linear order of genes on a chromosome The percentage of crossing-over for two traits is proportional to the distance between them on a chromosome Map Unit – a 1% frequency (chance) to cross over

They do not affect the organism itself but can be passed to offspring Mutations Germ-Cell Mutations – changes in nucleotide-base sequence that take place in an organism’s gametes They do not affect the organism itself but can be passed to offspring

They can affect an organism but will not be passed on to offspring Mutations Somatic-Cell Mutations – changes in nucleotide-base sequence that take place in an organism’s body cells They can affect an organism but will not be passed on to offspring

Chromosomal Mutations Chromosome Mutation – changes in the structure of a chromosome or complete loss or gain of a chromosome

Types of Chromosomal Mutations Deletion – loss of a piece of a chromosome Inversion – chromosome segment breaks off, flips around, and reattaches

Types of Chromosomal Mutations Translocation – a piece of chromosome breaks off and reattaches to a non-homolog Nondisjunction – a chromosome fails to separate from its homologue during meiosis Causes one gamete to receive an extra chromosome and one gamete to receive no copies

Human Genetics KEY CONCEPT Geneticists analyze genetic data to track the factors that influence human genetic traits and their inheritance

Pedigrees Pedigree – a diagram (tree) that shows how a trait is inherited over several generations Squares are males Circles are females Filled symbols have the trait/condition Empty symbols do not have trait or condition

Patterns of Inheritance – the expression of genes over generations Pedigrees help interpret these patterns Carrier – an organism that does not express the phenotype for a trait, but carries one recessive allele A carrier can pass the allele to an offspring who might wind up showing the phenotype

Complex Characters Complex Characters – traits influenced strongly by both the environment and by genes Read the first two paragraphs on page 243 X-linked Traits – complex characters that are determined by genes found on the X-chromosome Sex-Influenced Traits – autosomal traits where the same genotype in males and females will show as different genotypes

Genetic Disorders We will go over Table 12-1 on page 246 and do a Punnett square for Tay-sachs to see how a carrier functions

Genetic Disorders

Pedigree Analysis

Pedigree Analysis