Phenotype & Pedigrees

Human Genetics: Karyotypes 46 TOTAL 23 homologous pairs 46 TOTAL Chromosomes 23 homologous pairs

What is the difference between an Autosome and a Sex-chromosome? Autosomes are the first 22 homologous pairs of human chromosomes that do not influence the sex of an individual. Sex Chromosomes are the 23rd pair of chromosomes that determine the sex of an individual.

Phenotype can depend on interactions of alleles. In incomplete dominance, neither allele is completely dominant nor completely recessive. Heterozygous phenotype is intermediate between the two homozygous phenotypes Homozygous parental phenotypes not seen in F1 offspring

The environment interacts with genotype. Phenotype is a combination of genotype and environment. The sex of sea turtles depends on both genes and the environment Height is an example of a phenotype strongly affected by the environment.

Linkage maps estimate distances between genes. The closer together two genes are, the more likely they will be inherited together. Cross-over frequencies are related to distances between genes. Linkage maps show the relative locations of genes.

Gene Mapping https://www.youtube.com/watch?v=TU44tR0hJ8A (9 min)

Cross-over frequencies can be converted into map units. gene A and gene B cross over 6.0 percent of the time gene B and gene C cross over 12.5 percent of the time gene A and gene C cross over 18.5 percent of the time

Human genetics follows the patterns seen in other organisms. The basic principles of genetics are the same in all sexually reproducing organisms. Inheritance of many human traits is complex. Single-gene traits are important in understanding human genetics.

A family history of a genetic condition PEDIGREE CHARTS A family history of a genetic condition © 2007 Paul Billiet ODWS

Pedigree video https://www.youtube.com/watch?v=Wuk0W10EveU

What is a pedigree chart? Pedigree charts show a record of the family of an individual They can be used to study the transmission of a hereditary condition They are particularly useful when there are large families and a good family record over several generations.

Studying human genetics You cannot make humans of different types breed together Pedigree charts offer an ethical way of studying human genetics Today genetic engineering has new tools to offer doctors studying genetic diseases A genetic counsellor will still use pedigree charts to help determine the distribution of a disease in an affected family

Symbols used in pedigree charts A marriage with five children, two daughters and three sons. The eldest son is affected by the condition. Eldest child  Youngest child Normal male Affected male Normal female Affected female Marriage

A pedigree is a chart for tracing genes in a family. Phenotypes are used to infer genotypes on a pedigree. Autosomal genes show different patterns on a pedigree than sex-linked genes.

If the phenotype is more common in males, the gene is likely sex-linked.

Organising the pedigree chart A pedigree chart of a family showing 20 individuals

Organising the pedigree chart Generations are identified by Roman numerals I II III IV

Organising the pedigree chart Individuals in each generation are identified by Arabic numerals numbered from the left Therefore the affected individuals are II3, IV2 and IV3 I II III IV

If the phenotype is more common in males, the gene is likely sex-linked.

Several methods help map human chromosomes. A karyotype is a picture of all chromosomes in a cell. X Y

Karyotypes can show changes in chromosomes. deletion of part of a chromosome or loss of a chromosome large changes in chromosomes extra chromosomes or duplication of part of a chromosome

Incomplete Vs. Co-dominance Codominance - A form of inheritance in which both alleles are equally shown. Incomplete dominance - A form of inheritance in which the heterozygous alleles are both expressed, resulting in a combined phenotype. Most commonly found in plants. A red and a white allele gives pink. If it were codominance, you would see the red and white colors.

Codominant alleles will both be completely expressed. Codominant alleles are neither dominant nor recessive. The ABO blood types result from codominant alleles. Many genes have more than two alleles.

Test Cross Used to determine an organisms genotype. Either Bb or BB Always a dominant unknown mated with pure recessive B? X bb

Go to Page 188 in textbook Complete questions 1-4 Remember the genotypes you are using are: Rrtt x RrTT resulting in Rt Rt rt rt x RT RT rT rT RT rT Rt RRTt RRTt rt RrTt rrTt 3:1 ratio