Genetics: The Science of Heredity

Genetics Vocabulary Heredity- the passing of physical characteristics from parent to offspring through joining of sex cells (sperm and egg) Trait- different forms of a physical characteristic (phenotype) Example: height, eye color, disease

Genetics Vocabulary Hybrids - offspring from parents with different traits. Purebred - the offspring of many generations that have the same trait ( breed “true”) P Generation: parental generation F1 Generation: -First filial (filia and filius in Latin means daughter and son) -offspring from P generation F2 Generation: -Second filial - offspring from the F1 generation

Generations P Generation F1Generation F2 Generation

Video Break- What is a genetic counselor? Geneticist: Scientist who studies heredity

Homunculus (1695) Belief that a miniature fetus lived in every sperm

Gregor Mendel (The Father of Genetics) experimented with thousands of pea plants to understand the process of heredity during the mid 19th century.

Why Pea Plants? They grow and reproduce quickly. Phenotypes are easily observed Can cross- pollinate flowers

Flower Structure and Function Stamen- produces male sex cells, pollen Pistil- produces female sex cells, eggs

Mendel cross–pollinated purebred pea plants of contrasting traits. pistil stamen Produces male sex cells, pollen produces female sex cells, eggs Cross Pollination Tall Purebred Short Purebred

Mendel and Cross Pollination Animation Browse the website for more useful information!

Mendel Studied a Variety of Pea Plant Phenotypes

- Mendel’s Work Mendel’s Experiments Phenotype Observed: Height 3:1 ratio of Tall to Short Purebreds The short trait reappeared in about ¼ of the plants. All offspring tall! Why did this happen?

Mendel's Conclusions: "heritable factor" for short flowers was not lost in F1 rather, the "heritable factor" for short flowers was "masked" by the tall “heritable factor” Mendel could not accurately explain how these traits were inherited Mendel didn't know about genes at this time. These heritable factors were later discovered to be composed of DNA. When was DNA discovered?

Mendel RapMendel Rap Video Break

Modern Genetics What we know today…

Alleles are a different form of a gene.  Gene- section of DNA that controls traits  Allele- different forms of a gene  For example, the gene that controls stem height in peas has one allele for tall stems and one allele for short stems. GeneAllele 2Allele 1

A Lineup of Genes Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others. Different alleles Same alleles

Dominant and Recessive Alleles – Dominant allele- trait always shows up in the organism – represented by the CAPITAL LETTER of the dominant trait (W) – Recessive allele- trait is “hidden” whenever the dominant allele is present – represented by a lower case version of the dominant allele (w)

How come the parents only contribute one allele and not both alleles to their offspring?

Male Meiosis Female Meiosis WW ww WwWw Possible Male GametePossible Female Gamete LAW OF SEGREGATION The two alleles for each gene segregate during gamete production (meiosis). LAW OF SEGREGATION The two alleles for each gene segregate during gamete production (meiosis). W w w W WW ww Fertilization

Alleles combine during fertilization to form genotypes. Phenotype: Genotype: genetic makeup, the possible allele combinations W Homologous Pair of Chromosomes w Widow’s Peak dominant allele for a widow’s peak (from male gamete) recessive allele for straight hairline (from female gamete) Genotype: WwWw

Genotype expresses phenotype.

Alleles combine during fertilization to form genotypes. Color Gene Chromosome Color Gene Chromosome Female Male BB b b Bb

In a human, alleles from 23 homologous chromosomes pair up to form all the organism’s genotypes.

Possible Allele Combinations (Genotypes) and their Phenotypes GenotypeDescription Phenotype (What trait is expressed?) Homozygous Recessive Homozygous DOMINANT Heterozygous recessive allele DOMINANT allele DOMINANT allele ss (purebred) SS (purebred) Ss (hybrid)

Check for Understanding Write the following allele combinations using the letter H. – Homozygous Dominant – Homozygous recessive – Heterozygous HH hh Hh

Probability and Heredity The allele that each parent will pass on to its offspring is based on probability. Probability is the number that describes how likely an event will occur. When a coin is tossed into the air, what is the probability that it will land on heads? ½, 1 out of 2 or 50 % 1 out of 4 = 25 % 2 out of 4 = 50 % 3 out of 4 = 75 % 4 out of 4 = 100 %

Punnett Squares shows all the possible combinations of alleles that can result after fertilization used to determine the probability of a particular phenotype and genotype

In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele and r represents the recessive wrinkled allele. How to Make a Punnett Square Male Female Dominant Trait (Round Seeds) ¾= 75 % Chance Recessive Trait (Wrinkled Seeds) ¼= 25% chance

Meiosis and Punnett Squares Possible zygotes that may turn into offspring *Notice, the dominant allele is always written before the recessive allele.

P p p PpPp pp PP PpPp *Notice, the dominant allele is always written before the recessive allele. Use the following information to set up a Punnett Square in the blank space below: The dominant allele for flower color is purple (P). The recessive allele for flower color is white (p). The male and female are both heterozygous for flower color. P p Answer these questions after you complete the cross… 1. List all the genotypes that would result in offspring with a purple phenotype: 2. List all the genotypes that would result in offspring with a white phenotype: 3. What is the probability of purple flowered offspring? White colored offspring? PP and Pp pp Purple: ¾ = 75 % chance White: ¼ = 25 % chance

p P Pp P p PPPp pp Male Gametes and their possible alleles Female Gametes and their possible alleles Possible Zygotes (offspring) *Notice, the dominant allele is always written before the recessive allele. RESULTS: PP, Pp, Pp = Purple (3) ¾ = 75 % chance pp = white (1) ¼ = 25 % chance Taking a Closer Look…

Click here to watch the BrainPop on Heredity! Username: ronkonkoma Password: brainpop

Good Overview...click here

How to Make Punnett Squares...a good review How to Make Punnett Squares...a good review

Crash Course in Heredity

Gregor Mendel: Great Minds

Punnett Squares with the Amoeba Sisters!