mendel & heredity. are you ready for this? can you… define the term gamete. summarize the...
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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 _______