MENDEL & HEREDITY

Are You Ready For This? Can You… Define the term gamete. Summarize the relationship

between chromosomes and genes? Differentiate between autosomes

and sex chromosomes? Describe how independent

assortment during meiosis contributes to genetic variation?

Heredity – the passing of traits from parent to offspring

Genetics – Branch of Biology that focuses on heredity

Gregor Mendel Austrian monk Bred different

varieties of pea plants Was the 1st person to

develop rules to predict the outcome, or patterns of heredity

Why Pea Plants?

A. Have many different traits that have two clearly different forms that are easy to tell apart.

Example ) TRAIT : Color FORM: Purple or WhiteB. Mating can be easily controlledC. Small, grow easily, mature quickly,

produce many offspring

Mendel’s Experiments

Monohybrid Cross – Involved one pair of contrasting traits

Cross Pollination – allowed him to mate two plants with different characteristics and to study the results.

Observations:

What happened to the white flowers?

All results for traits in the F2 generation were in a 3:1 ratio.

Mendel’s Hypotheses

Inheritance is determined by factors that are passed from one generation to the next, called genes.

There are alternative versions of the genes, called alleles.

Example: The gene that controls plant height comes in two forms; tall and short

Principle of Dominance – Some alleles are dominant and some are recessive.

Dominant = uppercase letterRecessive = lowercase letter

Genes and Dominance You have 2 alleles for many traits in

your body (one from your mom and one from your dad)

If you have a dominant allele (capital letter), you will always show that characteristic. In order to show a recessive characteristic, the dominant allele must be missing.

Example TRAIT = Hair Texture

Dominant Allele (H) - curly hairRecessive Allele (h) - straight hair

Since you have two alleles, there are three possible combinations that you may have:

HH – curly hairHh – curly hairhh – straight hair

TerminologyTwo of the same alleles (HH, hh) is called homozygous, or pure

Two different alleles (Hh) is called heterozygous, or hybrid

Phenotype & GenotypePhenotype – physical characteristicsExample – straight hair, brown eyes, tall

Genotype – genetic makeup of an individualExample – hh, Bb, TT

Mendel’s Ideas Laws of HeredityLaw of Segregation – Two alleles for a trait segregate when gametes are formed during meiosis

Law of Independent Assortment – The alleles of different genes separate independently from one another

Do Now

In humans, polydactyl is a recessive genetic trait that causes humans to have extra digits. Normal number of digits is represented by a (P) and polydactyl is represented by a (p)

1. What are the 3 possible combinations of alleles?

2. For each set of words, write the matching genotype: Homozygous recessive ______ Hybrid ______ Pure dominant _______ Heterozygous _______