Phenotype Pedigrees Human Genetics Karyotypes 46 TOTAL 23

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 Sexchromosome? • Autosomes are the first 22 homologous pairs of human chromosomes that do not influence the sex of an individual. • Sex Chromosomes are the 23 rd 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 F 1 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=TU 44 t. R 0 h. J 8 A (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.

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

Pedigree video • https: //www. youtube. com/watch? v=Wuk 0 W 10 Eve. U

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

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 IV

Organising the pedigree chart • Individuals in each generation are identified by Arabic numerals numbered from the left • Therefore the affected individuals are II 3, IV 2 and IV 3 I II 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. XY

• 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 Rr. TT resulting in Rt Rt rt rt RT RRTt Rr. Tt r. T RRTt rr. Tt x RT RT r. T 3: 1 ratio