GeneticsGenetics

Is the branch of Is the branch of biology dealing biology dealing

with the principals with the principals of variationof variation

Who Am I?

Early ideas about HeredityEarly ideas about Heredity

There are only two There are only two things, science and things, science and opinion; opinion; 

the former begets the former begets knowledge, the knowledge, the latter ignorance. latter ignorance.

……HippocratesHippocrates

HippocratesHippocrates

He believed that every part of the He believed that every part of the body produced the seeds of the body produced the seeds of the parents which fused together to parents which fused together to give rise to a new individualgive rise to a new individual

Hippocrates is known as the father Hippocrates is known as the father of scientific medicine.of scientific medicine.

Hippocrates wrote the physicians Hippocrates wrote the physicians oath called the Hippocratic Oath oath called the Hippocratic Oath that establishes the standards, even that establishes the standards, even today, how the physician should today, how the physician should treat their patient.treat their patient.

AristotleAristotle

AristotleAristotle waswas one of the two most important one of the two most important philosophers of ancient timesphilosophers of ancient times (the other was (the other was PlatoPlato). ). He was born in Stagira in the north of Greece in 367 He was born in Stagira in the north of Greece in 367 BC. When he was 17 he went to study at Plato's BC. When he was 17 he went to study at Plato's Academy in Athens, where he remained as a student Academy in Athens, where he remained as a student and teacher for 20 years. For three years he served as and teacher for 20 years. For three years he served as Alexander the Great's private tutor. In 335 Aristotle Alexander the Great's private tutor. In 335 Aristotle returned to Athens, where he founded his school, the returned to Athens, where he founded his school, the Lyceum. In 323, after the death of Alexander the Great, Lyceum. In 323, after the death of Alexander the Great, Aristotle felt that Athens was dangerous and moved to Aristotle felt that Athens was dangerous and moved to Chalcis, where he died at the age of 62. Chalcis, where he died at the age of 62.

AristotleAristotle

He believed that male He believed that male and female semen and female semen mixed upon conception.mixed upon conception.

Sperm (angular) and mature fertilized egg of Ascaris worm

HarveyHarvey

Embryo formed in stages and its development Embryo formed in stages and its development was affected by factors both inside and outside was affected by factors both inside and outside the mother (known as epigenesis)the mother (known as epigenesis)

EpigenesisEpigenesis – Development of an individual – Development of an individual and/or the external environment as a result and/or the external environment as a result from interaction between an individual’s from interaction between an individual’s GENESGENES, external environment and internal , external environment and internal environment.environment.

Antony van Leeuwenhoek Antony van Leeuwenhoek

Believed that embryos Believed that embryos were preformed in the were preformed in the male semen and that the male semen and that the only involvement only involvement females has was in the females has was in the uterus where the uterus where the embryo developedembryo developed

PangenesisPangenesis

Males and females formed genes in every Males and females formed genes in every organ .organ .

These genes moved through the blood to the These genes moved through the blood to the genitals into the childrengenitals into the children

A theory of heredity proposed by Charles A theory of heredity proposed by Charles Darwin Darwin

DarwinDarwin

Offspring had variations Offspring had variations but was unable to but was unable to explain the basis of explain the basis of heredityheredity

He wrote the “Origin of He wrote the “Origin of Species”Species”

Blending TheoryBlending Theory

Sperm and egg mix Sperm and egg mix together to give together to give offspring that were a offspring that were a blend of the parent’s blend of the parent’s characteristics. characteristics.

red flower + white red flower + white Flower = PINK flowerFlower = PINK flower

Gregor MendelGregor Mendel

Mendel's laws form the theoretical basis of Mendel's laws form the theoretical basis of our understanding of the genetics of our understanding of the genetics of inheritance. inheritance.

Mendel made two innovations to the science Mendel made two innovations to the science of genetics: of genetics:

1.1. developed pure lines developed pure lines

2.2. counted his results and kept statistical notes counted his results and kept statistical notes

Mendel accomplished most of his work with Mendel accomplished most of his work with garden peas, with clear cut characteristics so garden peas, with clear cut characteristics so they could be easily followedthey could be easily followed

Each of his 7 chosen traits had only 2 possible Each of his 7 chosen traits had only 2 possible variations: round and wrinked seeds, gellow variations: round and wrinked seeds, gellow and green colour, tall and short etc. Fig. 4.8 in and green colour, tall and short etc. Fig. 4.8 in your textyour text

Seed Shape: Wrinkled and Round seeds.

                  

What is an ALLELEWhat is an ALLELE

One of the several alternative forms of a specific One of the several alternative forms of a specific gene, each possessing a unique nucleotide sequence. gene, each possessing a unique nucleotide sequence.

For example, the gene for human eye color might be For example, the gene for human eye color might be expressed in several forms: blue, brown, green, etc. expressed in several forms: blue, brown, green, etc. When a person has one gene for blue eyes and one When a person has one gene for blue eyes and one gene for brown, they have two alleles of that gene for brown, they have two alleles of that particular gene. Evolution proceeds by the change in particular gene. Evolution proceeds by the change in the how frequent alleles appear in a population over the how frequent alleles appear in a population over the course of time. the course of time.

tall and dwarf are the alleles for the height of a pea tall and dwarf are the alleles for the height of a pea plant.plant.

MatingMating

Mendel mated pure (homozygous) individulas.Mendel mated pure (homozygous) individulas. He called this the P generation or the parent He called this the P generation or the parent

generation.generation. What happened when Mendel crossed pure tall What happened when Mendel crossed pure tall

plants with pure short plants? Fig 4.9plants with pure short plants? Fig 4.9

Symbolic representation of the cross between tall and short pea plants

Parental Generation DD x dd

           

Parental Gametes D   d

         

F1 Genotype Dd

New TermsNew Terms

Mendel coined two new terms. Mendel coined two new terms. DominantDominant

the allele that expresses itself at the expense of an the allele that expresses itself at the expense of an alternate allele; the phenotype that is expressed in the alternate allele; the phenotype that is expressed in the F1 generation from the cross of two pure linesF1 generation from the cross of two pure lines

RecessiveRecessive an allele whose expression is suppressed in the presence an allele whose expression is suppressed in the presence

of a dominant allele; the phenotype that disappears in of a dominant allele; the phenotype that disappears in the F1 generation from the cross of two pure lines and the F1 generation from the cross of two pure lines and reappears in the F2 generationreappears in the F2 generation

Punnett SquarePunnett Square The Punnett square is a mathematical tool The Punnett square is a mathematical tool

used by geneticists to show allelic used by geneticists to show allelic combinations of gametes and to predict combinations of gametes and to predict offspring ratios. offspring ratios.

To fill in the squares bring the symbols down To fill in the squares bring the symbols down from the top of the columns and write that from the top of the columns and write that symbol in each square of the column. Also, symbol in each square of the column. Also, bring the symbols across each row and write bring the symbols across each row and write that symbol in each square of the row. These that symbol in each square of the row. These filled squares are the F1 generation's gene filled squares are the F1 generation's gene combinations. They are the result of the combinations. They are the result of the parent's donation of alleles. In this case, all the parent's donation of alleles. In this case, all the F1 generation is Gg or heterozygous. F1 generation is Gg or heterozygous.

Principal of DominancePrincipal of Dominance

When individuals with contrasting traits are When individuals with contrasting traits are crossed, the offspring will express ONLY the crossed, the offspring will express ONLY the dominant trait (allele).dominant trait (allele).

Dominance is notes with uppercase letters Dominance is notes with uppercase letters (TT = tall) (TT = tall) homozygous dominanthomozygous dominant

and recessiveness is noted with lowercase and recessiveness is noted with lowercase letters (tt = short) letters (tt = short) homozygous recessivehomozygous recessive

Tt = tall but Tt = tall but heterozygous heterozygous or or hybridhybrid for that for that trait trait

Same or different alleles?Same or different alleles?

HomozygoteHomozygote an individual which contains only one allele at an individual which contains only one allele at

the allelic pair; for example the allelic pair; for example DDDD is homozygous is homozygous dominant and dominant and dddd is homozygous recessive; pure is homozygous recessive; pure lines are homozygous for the gene of interestlines are homozygous for the gene of interest

HeterozygoteHeterozygote an individual that contains two different alleles an individual that contains two different alleles

at the allelic pair; for example the at the allelic pair; for example the DdDd

heterozygoteheterozygote

Back to Mendel’s experimentBack to Mendel’s experiment

The offspring he got from this mating of the The offspring he got from this mating of the P1 generation is called theF1 generation.P1 generation is called theF1 generation.

He then mated 2 F1 individuals, and the result He then mated 2 F1 individuals, and the result was a F2 generationwas a F2 generation

What did he find?What did he find?

The following Punnett square shows the F2 generation created by selfing

the F1 plants.

D d

Union of gametes D DD

(tall) Dd

(tall)

occurs at random d Dd

(tall) dd

(dwarf)

Tall or DwarfTall or Dwarf

This could also be done with smooth This could also be done with smooth vs. round seedsvs. round seeds

Findings of F1 matingsFindings of F1 matings

Mendel saw that the F2 generation ressembled Mendel saw that the F2 generation ressembled one parent from the P1 generation 75% of the one parent from the P1 generation 75% of the time and the other parent of the P generation time and the other parent of the P generation 25% of the time25% of the time

This is known as the Medelian phenotypic This is known as the Medelian phenotypic ratio (3:1)ratio (3:1)

Genotype and PhenotypeGenotype and Phenotype

The Punnett Square allows us to visualize The Punnett Square allows us to visualize specific genetic ratios. specific genetic ratios.

F2 Genotypic ratio: F2 Genotypic ratio:

1 1 DDDD : 2 : 2 DdDd : 1 : 1 dd dd (or 3 (or 3 D_D_ : 1 : 1 dddd) )

F2 Phenotypic ratio: F2 Phenotypic ratio: 3 tall : 1 dwarf 3 tall : 1 dwarf

What you see and what it really is?What you see and what it really is?

PhenotypePhenotype the appearance of the trait in an organismthe appearance of the trait in an organism

GenotypeGenotype the specific allelic combination for a certain the specific allelic combination for a certain

gene or set of genesgene or set of genes or genetic make-up of an or genetic make-up of an organism.organism.

Allelic ExpressionAllelic Expression

When 2 alleles are present and there is a When 2 alleles are present and there is a dominant one and a recessive one in your dominant one and a recessive one in your Punnett Square, the dominant allele may Punnett Square, the dominant allele may prevent the expression of the recessive allele prevent the expression of the recessive allele in the PHENOTYPE (masks it from being in the PHENOTYPE (masks it from being seen)seen)

Law of SegregationLaw of Segregation

Mendel's First Law Mendel's First Law Inherited traits are determined by pairs of Inherited traits are determined by pairs of

genes (allelic pairs)genes (allelic pairs) These genes segregate in the gametes in the These genes segregate in the gametes in the

sex cells either the sperm or the egg from sex cells either the sperm or the egg from the male and femalethe male and female

ProbabilityProbability

Is the chance or likelihood of a particular Is the chance or likelihood of a particular outcome usually expressed as a ratio!outcome usually expressed as a ratio!

The probability of one event or another event The probability of one event or another event happening is the sum of their individual happening is the sum of their individual probabilities.probabilities.

EX: heads 50%, tails 50%EX: heads 50%, tails 50% Chances of heads or tails is 100%Chances of heads or tails is 100%