GENETICS

Gregor Mendel Genetics is the study of heredity. Gregor Mendel (1860 ’ s) discovered the fundamental principles of genetics by breeding garden peas.

Mendel cross- pollinated pea plants He cut away the male parts of one flower, then dusted it with pollen from another

What did Mendel conclude? He concluded that factors are passed from one generation to the next.

The Principle of Dominance Alleles 1.Alternative forms of genes. 2.Units that determine heritable traits. Paternal Maternal eye color locus B = brown eyes eye color locus b = blue eyes The Principle of Dominance – some alleles are dominant and other are recessive.

Dominant and Recessive alleles Dominant alleles – upper-case a. homozygous dominant (BB – Brown eyes) Recessive alleles – lower case a. homozygous recessive (bb – blue eyes) b. Heterozygous (Bb – Brown eyes)

Phenotype vs. Genotype Outward appearance Physical characteristics Examples: 1.Brown eyes2.blue eyes Arrangement of genes that produces the phenotype Example: 1.TT, Tt 2. tt

Segregation Alleles separate during meiosis

Recessive traits show up about 1/4 th of the time. Because there is only a 25% chance that two recessive alleles will be paired together.

Punnett square A Punnett square is used to show the possible combinations of gametes. Monohybrid Cross

Example:Cross between two heterozygotes for brown eyes (Bb) BB = brown eyes Bb = brown eyes bb = blue eyes B b Bb Bb x Bb male gametes female gametes

Monohybrid Cross BB Bb bbB b Bb Bb x Bb 1/4 = BB - brown eyed 1/2 = Bb - brown eyed 1/4 = bb - blue eyed 1:2:1 genotype 3:1 phenotype

Dihybrid Cross

RYRyrYry RYRy rY ry

RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry

Dihybrid Cross Example:cross between round and yellow heterozygous pea seeds. R= round r= wrinkled Y= yellow y= green RY Ry rY ry RY Ry rY ry RY Ry rY ry x RY Ry rY ry possible gametes produced RrYyRrYy RrYy x RrYy

Independent Assortment Chromosomes separate independently of each other Bb diploid (2n) B b meiosis I B B b b sperm haploid (n) meiosis II Bb Ff BFBF BfBf bfbf B F Bb Ff Bb Ff This means all gametes will be different!

Independent Assortment Genes for different traits can segregate independently during the formation of gametes without influencing each other Question: How many gametes will be produced for the following allele arrangements? Remember: 2 n (n = # of heterozygotes) 1.RrYy 2.AaBbCCDd 3.MmNnOoPPQQRrssTtQq

Answer: 1. RrYy: 2 n = 2 2 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2 n = 2 3 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2 n = 2 6 = 64 gametes

Incomplete Dominance One allele is not completely dominant over another Rr r r RR All Rr = pink (heterozygous pink) produces the F 1 generation

Codominance Both alleles are expressed Example: blood 1.type A= I A I A or I A i 2.type B= I B I B or I B i 3.type AB= I A I B 4.type O= ii Black cow + white cow = spotted cow

Which shows more genetic variation. (more combos?) Male CC with female Cc Male cc with female Cc C c cc C c CC

Genetic Engineering

Gene Therapy

Is cloning a possibility? Is it right to use cloning to create an entirely new human being? Is it ethical to create an embryonic copy of John Doe to supply cells to keep John alive? Does a multicellular ball of tissue -- an embryo -- have the same rights and status as a human being?

How does Mendel ’ s principles apply to organisms The basic principals can be applied to humans as well as any other living organism.

Consider this Punnett square: Consider this Punnett square:

Many traits are controlled by multiple alleles or multiple genes. Many traits are controlled by multiple alleles or multiple genes. – Multiple alleles (more than 2 choices) – Polygenic (multiple genes control a single trait)

Multiple alleles: the case where three or more alleles of the same gene exist. Remember, an organism will have only two of these alleles (one from mom and one from dad). the case where three or more alleles of the same gene exist. Remember, an organism will have only two of these alleles (one from mom and one from dad). – Examples: Coat color in rabbits, blood type in humans

Multiple alleles:

Polygenic traits: traits that are determined by alleles from more than one gene; these traits usually have a range of phenotypes traits that are determined by alleles from more than one gene; these traits usually have a range of phenotypes – Examples: skin color in humans, height in humans

Mapping Genes It ’ s easy to imagine that genes on different chromosomes assort independently, but what about genes that occur on the same chromosome? Don ’ t they always appear together? It ’ s easy to imagine that genes on different chromosomes assort independently, but what about genes that occur on the same chromosome? Don ’ t they always appear together? Not always due to crossing over. Genes that occur together on a chromosome will be separated when homologous chromosomes exchange genes. Not always due to crossing over. Genes that occur together on a chromosome will be separated when homologous chromosomes exchange genes. The frequency of genes occurring together can help us generate a gene map. The frequency of genes occurring together can help us generate a gene map.

The more often two genes occur together, the closer they are to each other on the chromosome. The more often two genes occur together, the closer they are to each other on the chromosome. – If the genes are never separated by crossing over, they always occur together. All offspring will look like one of the parents (in reference to the genes in question).

– If half of the offspring are parental and half are recombinations of the parents (in reference to the genes in question), then they are said to be independent. This means they are either on separate chromosomes or they are almost always separated during meiosis. – You will learn to calculate distances and create a map in AP Bio, or in college

Human chromosomes 2.There are two types of chromosomes. a.Autosomes: Of the 46 chromosomes, 44 of them (22 pairs of chromosomes) are called autosomes (non-sex chromosomes). b.Sex chromosomes: The last two chromosomes are called the sex chromosomes because they determine the sex of the person. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

3.Gametes a.All gametes are haploid. In humans, that means each egg cell and each sperm cell has 1 copy of each chromosome for a total of 23 chromosomes. i.Egg cells: All human egg cells carry 23 chromosomes, one of which is a single X chromosome. This is written as 23, X. ii.Sperm cells: In males, there are two types of sperm cells- one carries an X chromosome (23, X) and one carries a Y chromosome (23, Y).

iii.When a sperm and egg cell combine, half of the time the fertilized eggs (also called zygotes) are female (46, XX) and half of the time they are male (46, XY). X X X Y XX XY female male sperm eggs

Sex Linked traits: traits that are determined by alleles that are found on the X or Y chromosome. – The Y chromosome is shorter and does not carry all the same alleles as the X chromosome.

– Females are XX and males are XY. – Females can be homozygous or heterozygous for a trait carried on the X chromosome, but males (having only one X chromosome) are hemizygous.

– If they inherit a defective gene from the parent, then they will exhibit the trait because they cannot inherit a second gene to mask it. – Conversely, a healthy male cannot be “ hiding ” a bad recessive allele because they only have one X chromosome.

Example of a sex-linked Punnett square: – X B X b (heterozygous female with normal vision) crossed to X B Y (hemizygous male with normal vision) XBYXBY XBYXBY XbYXbY X B X B X b Y XBXB XBXB XbXb

Genetics and the Environment Characteristics are determined by both genes and the environment. Characteristics are determined by both genes and the environment. External: While genes will influence the height of a plant, the amount of water, sun, and other climate conditions will also affect the height. External: While genes will influence the height of a plant, the amount of water, sun, and other climate conditions will also affect the height.

Genetics and the Environment Internal: There are recent findings that proteins involved with DNA can turn genes on or off based on environmental factors. Internal: There are recent findings that proteins involved with DNA can turn genes on or off based on environmental factors. – Certain chemical exposure can turn genes on or off (make the traits show up or not) for generations after exposure, but there are no changes to the DNA (no mutations). – This new understanding of how genes are expressed is called epigenetics.