What is Genetics? Genetics The study of how heredity information is passed from parents to offspring. The Modern Theory of Evolution =

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1 What is Genetics? Genetics The study of how heredity information is passed from parents to offspring The Modern Theory of Evolution = Genetics + Darwin s Theory of Natural Selection

2 Gregor Mendel Father of Genetics Studied inheritance of traits in pea plants Published research shortly after Darwin s book (but it was in an obscure journal) He received credit for his work in 1900 (15 yrs after his death) The pea traits he studied later became known as GENES Law of Dominance: (see below)

3 Each cell in your body contains a nucleus Each nucleus contains pairs of chromosomes What is a Gene? How many chromosomes do humans have? What cell type in your body only has ½ as many chromosomes? Chromosomes contain your DNA sequence A segment of DNA is called a gene A gene codes for a specific trait Cells > nucleus > chromosomes > genes (traits) > DNA segment

4 3,000,000,000 nitrogen base pairs make you who you are What is DNA? DNA stores information DNA = Deoxyribonucleic acid Subunit = nucleotides Nucleotides contain a nitrogen base 4 different nitrogen bases adenine (A) guanine (G) thymine (T) cytosine (C) Complimentary Strands (A-T) (G- C)

5 Genes and Chromosomes Genes are made up of complex combinations of the base pairs. A T G C Some genes code for proteins and enzymes. Some genes turn other genes on or off. Large sections of DNA code for NOTHING!

6 James Watson & Francis Crick (1953) Discovered the structure of a DNA molecule (double helix) which provided details on genes & how they work Name the DNA structure and draw an example on a blank page in your ISN

7 What is an Allele? Most organisms have TWO copies of every gene and chromosome (one from each parent) see picture below Alleles are the different forms of a gene for a specific trait Ex: flower color gene in pea plants contain a white allele and a purple allele Remember genes exist as pairs so often one allele is considered the dominant allele and the other the recessive allele Which is the purple allele?

8 Dominant & Recessive Alleles Dominant alleles are given a capital letter symbol Ex. Purple Flower = P Recessive alleles are given a lower case letter symbol Ex. White Flower = p Since genes are found in pairs, a pea plant could have the following combinations of alleles for flower color PP = purple Pp = purple pp = white The genetic make-up is called the genotype (PP, Pp, or pp) PP and pp is considered homozygous (all one allele type) Pp is considered heterozygous (two different allele types) The outward physical appearance for a gene is called the phenotype (purple or white), which is based on its genotype

9 Variation and Gene Pools A population is a group of individuals of the same species that interbreed. There common genes is called a gene pool. Relative (allele) frequency is the # of times an allele occurs in a gene pool compared to other alleles for the same gene. Based on genetics evolution is any change in the relative frequency of alleles in a population. Sources of Genetic Variation: mutation & sexual reproduction Does sexual reproduction change the allele frequency within a population? No it creates combinations of different phenotypes Types of Gene Variation: Single-Gene Traits and Polygenic Traits

10 Single-Gene Trait Widow s Peak Punnett Square B = purple b = white What are the chances of having the white phenotype? Flower Color What are the chances of carrying the white allele? What is the chance of having a heterozygous genotype? Read through the handout to complete a Punnett Square. As you read, complete the practice problem in your ISN notes page where you drew your DNA model

11 Polygenic Traits Controlled by 2 or more genes, each with 2 or more alleles creating many genotypes and phenotypes Examples Complexity of eye color Height in humans

12 DNA Code and Mutations The DNA Sequence shows how a species changes over time If a mutation (typo) occurs within the DNA sequence, genes can change causing alleles and traits to change Over time as more mutations accumulate the species changes