Genetics Heredity and Traits What is heredity Heredity

Genetics: Heredity and Traits

What is heredity? Heredity - the passing of characteristics from parents to offspring characteristics that are inherited are called traits. Genetics - the branch of biology that studies heredity Can you think of some traits that are inherited?

Genes are the ‘blue prints’ for protein products • • Genes are found on chromosomes. Genes makes products, like proteins. Proteins are the “building blocks” of all living organisms. Our proteins make us look like humans, not a mushroom.

How many nucleotides (bases) are in the Human Genome? ANSWER: ~ 3. 3 billion bases ~ 21, 000 genes

Who discovered genes? Gregor Mendel: a friar (monk) living in a monastery in Brno, Czech republic (1822 -1884; work 1850 s 1860 s) His work involved studying variation in pea plants (testing ~29, 000 plants)

Pea Plant Traits (Dominant versus Recessive) How did Mendel determine which trait was dominant?

Pea Plant Crosses (Example) • Mendel always investigated only a single trait (2 forms of the trait) • 1 st – Cross two ‘Pure Breeding’ parents • 2 nd – the F 1 generation would result in all being identical (All Dominant) • 3 rd – the F 2 generation would result in a 3: 1 ratio (3 Dominant: 1 Recessive)

But why? • Why are all the F 1 plants ‘Tall’ (not short, or a mixture of both)? • How are some of the F 2 plants ‘Short’? They disappeared in the F 1, and are back again. • The way an organism looks is referred to as a ‘Phenotype’.

Let’s look at this a little differently… • Instead of “phenotype” (Large versus Short), lets compare “genotypes” (number and versions of a gene). • First, how many copies of a gene do most organism have (including peas)? (HINT – It is equal to the number of parents). Yes – 2 copies!

Let’s look at this a little differently… • CHECK – We have 2 copies of all genes! • Second, how many different versions of a gene (also called “alleles”) do we have? (HINT – It is equal to the number of different phenotypes). Yes – 2 Versions (Alleles)!

Let’s redo our previous analysis of Mendel’s cross using genotypes What do we know? 1. Parents were purebreds. 2. We have two copies of all genes. 3. There are two versions of all genes. 4. Mendel was following one trait at a time. What would Tt look like (phenotype)? T = Tall and t = Short HINT: Dominant

F 1 Generation: All Tall Plants Yes - All F 1 Plants are ‘Tall’ Is it possible to have ‘Short’ F 1 plants? What are all the genotypes possible for the F 2 generation? Phenotypes? DRAW A PUNNETT SQUARE BEFORE YOU MOVE TO THE NEXT SLIDE…

F 2 Generation: 3 Tall to 1 Short All F 1 Plants are ‘Tall’ F 2 Plants are both ‘Tall’ and ‘Short’ (3: 1 ratio)

Quickly - Let’s look at how gender is determined in Humans Male Female How many different copies of a gene do humans have? How many different chromosomes do males contribute? Females? What is the ratio of males versus females?

Quiz (no worries; not graded!) dominant ? recessive dominant ? recessive ?

Quiz (no worries; not graded!) What offspring do you get from a ‘Back-Cross’ (LL x Ll)? L = long stems l = short stems All Phenotypes? All Genotypes?

Final question… • Use Teammates Consult to discuss with your group what you have learned about heredity. Summarize your thoughts on your paper. Use as many vocabulary words as you can to support evidence of your learning.