Genetics

DNA Review

Mutations: Sex vs Body

Important Science Guy Gregor Mendel – father of genetics, he worked with peas in a monastary

Who was this Mendel and what the heck is he doing in a monastery? born in 1822 trained himself to be a naturalist early in life worked as a substitute science teacher failed the qualifying exams to be a regular high school teacher! joined a monastery in Brunn, Austria sent to Vienna U. to study science and math

Mendel’s first published work: "Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight! Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!! MendelWeb

The work of Gregor Mendel …he called them his children! worked with pea plants… Why pea plants??? There was a long-standing tradition of breeding pea plants at the monastery where Mendel lived and worked

So…they were readily available and they come in lots of varieties! …there were plants with different flower colors, seed color, flower position etc..

‘Brother Greg... We grow tired of peas again!!!’

And best of all… Pea plants flowers can reproduce by themselves This allowed Mendel to see if strains were true breeding and to produce hybrids

What the heck does that mean? True-breeding: when plants self pollinate, all their offspring will be identical to themselves Hybrid: when parents with different traits are crossed, this is what we call the offspring SO – he could see if the plants would produce offspring identical to themselves and how parents with different traits would affect the offspring

How Mendel made hybrids… He’d then tie little bags around the flowers to prevent contact with stray pollen.

Mendel’s hybridization experiments… Monohybrid crosses: Parental Generation True-breeding purple flower x True-breeding white flower F 1 generation All purple flowers (the hybrids) F 2 generation Allowed F 1 offspring to self-fertilize 705 purple 224 white

The results of Mendel’s monohybrid crosses led him to propose… 1.All organisms contain two “units of heredity” for each trait (alleles). 2.Dominant and recessive alleles… …and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive).

Alternative versions of genes (called alleles) account for the variations in inherited characteristics For each character an organism inherits two alleles, one from each parent If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s phenotype– the other (recessive) allele has no noticeable effect on the organism’s phenotype

The Law of Segregation – during gamete formation, these two alleles separate randomly into separate gametes, but each gamete gets one copy of each gene

A bit of genetic jargon… phenotype vs. genotype What the organism looks like What alleles the organism has - its genetic makeup

More jargon… Genes are usually controlled by two alleles – expressed by two letters These alleles may be dominant or recessive: –Dominant: allele that is expressed in the phenotype Expressed as a capital letter (A) –Recessive: alleles that is completely masked in the phenotype Expressed as a lower case letter (a)

More jargon… homozygous vs. heterozygous 2 of the same alleles: PP or pp 2 different alleles: Pp P p Sometimes refer to heterozygous individuals as carriers because they carry both the recessive and dominant allele and can give either to their offspring, but only express the dominant allele

A Punnett square… Gametes from one parent P p Gametes from other parent P p PP purple PpPp PpPp pp purple white Ratio: 3:1 or ¾ purple, ¼ white

A Punnett square

Let’s relate Mendel’s findings to what we now know about gamete formation True-breeding purple flower x True-breeding white flower PP p PPP p pppp all purple P P p

F 1 generation purple hybrid x purple hybrid P p P p P P P P pp pp PP pp PP (purple)Pp (purple)Pp - purplepp - white F2F2

Law of Independent Assortment States that each allele pair segregates independently during gamete formation AKA: Alleles for different genes separate independently (alone) during meiosis when egg and sperm cells are being made – so alleles for seed color wouldn’t affect alleles for seed coat

Activity: Cross the following alleles and determine the phenotypic and genotypic ratios. Genotypic ratio Phenotypic ratio AA x aa aa x Aa AA x Aa Aa x Aa

Activity Answers Genotypic ratio Phenotypic ratio 0:1:0 (hd:h:hr)1:0 (dom:rec) or all dominant AA x aa 0:1:1 (hd:h:hr)1:1 (dom:rec)aa x Aa 1:1:0 (hd:h:hr)1:0 (dom:rec) or all dominant AA x Aa 1:2:1 (hd:h:hr)3:1 (dom:rec)Aa x Aa

Pedigrees Geneticists tool These are family trees that describe the occurrence of heritable characters in parents and offspring across many generations

Pedigree