Genetics Chapters 6 and 7

Mendel’s Laws of Segregation Called: MENDEL’s 1st LAW 2 parts Organisms inherit two copies o each gene (alleles) one from each parent Organisms donate only one copy of each gene (allele) in their gametes. Thus the two copies segregate or separate during gamete formation

Law of Independent Assortment Called Mendel’s 2nd Law of Genetics Allele pairs separate independently of each other during gamete formation (meiosis) different traits appear to be inherited separately One trait did not necessarily effect the inheritance of another trait.

Dihybrid vs mono hybrid cross Monohybrid Cross: Crosses that examine the inheritance of only one trait. Dihybrid Cross: Crosses that examine the inheritance of two different traits

Autosomal vs. Sex linked Genes Gene Expression is often related to whether a gene is located on an autosomal chromosome or a Sex Linked Chromosome. Autosomal Chromosomes are all other chromosomes in your body except the one that determines sex. Easy to track on a pedigree if you know the gene is located on an autosomal Chromosome. A person who does not show the phenotype must have a homozygous recessive genotype. Any other genotype will produce the phenotype. If two parents who express the genotype have an offspring that does not—then both of the parents MUST be heterozygous. Both males and females can be carriers of autosomal disorders.

Autosomal vs. Sex Linked Genes Sex linked genes are located only on sex chromosomes. Recall that species have specialized sex chromosomes called X and Y. in mammals (and some other organisms XX genotype are female and XY genotype are Male A female can only pass on an X chromosome but a male can pass either an X or a Y. Genes on the Y chromosome are responsible for development of the male offspring. The have a specialized pattern of inheritance.

Sex Linked Patterns of Inheritance FOR MALES: Remember two copies of an autosomal gene are needed to effect the gene. Because males have only one alleles of each X and Y they express all of the alleles on both chromosomes. Which means all the alleles of sex linked genes in a male are recessive—they will all be expressed. If a male has a recessive allele for a sex linked disorder—he will express it. FOR FEMALES: only females can be carriers of sex linked disorders. They can be carriers because they have another allele to mask it.

The likelihood of inheriting a sex linked disorder depends on the sex of the child and on which parent carries the disease carrying allele. If only the mother has the allele and is a carrier, a child will have a 50% chance of inheriting the allele. A daughter who inherits it will not show the phenotype but the son will.

Further investigation and homework TURN TO PAGE 214 and 215 in your text book to investigate further, Other pages in the book that will help you 200-201 Section 7.4 starts on page 212.

Vocab to Know Incomplete Dominance Neither allele is completely dominant or recessive The heterozygous phenotype is somewhere in between the two homozygous phenotypes Please turn to pg 205 and sketch the example of the beta fish into your notes.

Vocab to Know Codominance Both alleles are expressed completely—but neither one is dominant or recessive Example red and white flowers that are crossed are codominant—the resulting flowers will have some red areas and some white areas. Another example: Blood Type Pg 205 example Blood type is also a multiple allele trait

Vocab to know Polygenic traits Traits produced by two or more genes Example: skin color Example on pg 206