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WHAT IS GENETICS? GENETICS is the study of how traits are passed from parent to offspring in the form of Genes.

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Presentation on theme: "WHAT IS GENETICS? GENETICS is the study of how traits are passed from parent to offspring in the form of Genes."— Presentation transcript:

1 WHAT IS GENETICS? GENETICS is the study of how traits are passed from parent to offspring in the form of Genes.

2 HISTORY! Gregor Mendel Born 1822 Austrian Monk
Examined reproduction of pea plants

3 Plants reproductive organs
are called FLOWERS A flower has both male and female parts. The pea plants Mendel was working with were typically TRUE-BREEDING, meaning they self-pollinated EX, TALL pea plants would always be pollinated by tall pea plants and produce tall offspring!

Genes – control a heritable feature (characteristic); Example: Hair color, seed shape, height; Allele – controls the variation of a feature (trait). Example: brown, blonde, black hair

5 REVIEW TIME: What are homologous chromosomes???

6 Homologous chromosomes may……
Both have the same alleles HOMOZYGOUS (aka: pure or true-breeding) Both have different alleles  HETEROZYGOUS (aka: hybrid)


8 Mendel’s Idea Cross two pea plants with different contrasting traits!
Ex: First cross : Crossed true breeding purple with true-breeding white plants. Called offspring F1 Generation Results were that offspring were_100% PURPLE_ Had the white allele disappeared????


10 Mendel’s Law of Dominance
some alleles over power others. So even if both alleles are present, we only “see” the dominant one. the “hidden” allele is called recessive This only applies to SOME genes, not all

11 Second cross  two of the purple F1 Offspring
Called offspring the F2 Generation Results 75 % purple 25 % were white White trait had reappeared!

12 “The Traits (genes) Mendel looked at

13 Mendel’s Law of Segregation
during meiosis, the pair of alleles in a parent will separate. Only ONE allele for EACH TRAIT will pass from each parent to the offspring

14 Ex. sugar beet preference.
dominant allele (A) prefers sugar beets recessive allele (a) does not. Heterozygote produces gametes 50% chance Get A Get a Question: If a heterozygous sugar beet eater marries a non-sugar beet eater, what possible offspring could they have?

15 Mendel’s Law of Independent Assortment
Alleles for different genes are passed to offspring independently of each other. The result is that new combinations of genes present in neither parent is possible. How many allele combinations could the following genotype produce? RRYY RRYy RrYy


17 Genetic Terms Diploid (2n)- Two sets of chromosomes.
Somatic Cells Haploid (n)- One set of homologous Chromosomes (gametes) Egg- Female haploid gamete Sperm- male haploid gamete

18 Parent – Seriously, you should know this
Meiosis – Cell division that produces haploid gametes Testes – Site of male meiosis Gamete – Haploid sex cell (sperm, egg, pollen)

19 Zygote- Single cell (result of sperm and egg)
Progeny - Offspring Offspring – see above Fertilization – gametes fuse into zygote Ovary- site of female meiosis - eggs

20 Genotype: the alleles that an organism has.
alleles are abbreviated using the first letter of the dominant trait. capital letter represents the dominant  ex: P for purple flower allele lower case represents the recessive.  ex: p for white flower allele

21 All diploid organisms have two alleles for each trait:
Can be two of the same alleles  Ex: PP or pp called Pure or Homozygous. OR Can be two different alleles  Ex: Pp described as Hybrid or Heterozygous

22 Phenotype: physical appearance
Examples: brown hair, widows peak, purple flowers the trait that “wins” in the case of complete dominance; depends on the combination of alleles GENOTYPE


24 P Generation: “parents;”
MENDEL’S CROSSES P Generation: “parents;” F1 Generation  offspring of P generation F2 Generation  offspring of F1 generation Punnet Squares  How we show allele combinations in crosses

25 Allele in Egg 1 Allele in Egg 2 Allele in sperm 1 Allele in sperm 2
Zygote formed if sperm 1 fertilizes egg 1 Allele in Egg 2 Allele in sperm 1 Allele in sperm 2 Zygote formed if sperm 2 fertilizes egg 1 Zygote formed if sperm 1 fertilizes egg 2 Zygote formed if sperm 2 fertilizes egg 2

26 Monohybrid Cross Tall vs. Short Example
Tall allele  T Short allele  t P Cross TT x tt F1 Generation Genotypes Phenotypes T T t t

27 F2 Generation F1 Generations 100% Tt Tt x Tt F2 Generation Genotypes-
Phenotypes- T t T t



30 Sample Problems Homozygous Tall x Heterozygous Tall
Heterozygous Tall x Homozygous Short

31 Probability Probability is only the LIKELIHOOD of an event happening.
It does not mean it is what HAS to happen Ex. Coin Toss. Two tosses, always one heads and one tails? What happens when we look at very large samples? Ex. Male/female ratio of a family vs. the world!

32 INHERITENCE PATTERNS Every gene demonstrates a distinct phenotype when both alleles are combined (the heterozygote) Complete dominance is when both alleles are present, only the dominant trait is seen. Incomplete dominance - when both alleles are present, the two traits blend together and create an intermediate trait


34 Inheritance Patterns:
Co-dominance - when both alleles are present, both traits are visible Different notation: Use first letter of the feature with a superscript for the trait. Example: CW or CR for white petals or red petals;

35 Women have two X’s but men only have one.
How do we deal with the genes on the X chromosome?

36 Probabilities Question 1: What is the probability of having a female offspring? Question 2: After having 4 sons in a row, what is the probability the next kid will be male? Question 3: What is the probability of having three daughters in a row?

37 Sex-Linked Traits Refers to traits coded by genes found on the X chromosome Females will have 2 copies of these genes Males will have 1 copy of these genes Significance??? If males get a bad (recessive) allele for a sex- linked trait, THEY WILL EXPRESS THE RECESSIVE TRAIT!

38 Example – Color Blindness
Seeing color (XC) is dominant to being color blind (Xc) Identify the sex and trait of the following: XCY XCXc XCXC XcXc XcY

39 XC Xc XC XC Xc XC Xc Y Y XC Y Cross Number 1:
What % chance of having color blind daughter? Son? XC Xc XC XC Xc XC Xc Y Y XC Y


41 Test cross: a cross that determines genotype of dominant parent
- Cross unknown dominant parent (possibilities BB or BB) with a recessive parent then analyze the offspring. Ex. B- Black Hair b- white hair You are given a black-haired guinea pig and need to determine whether homozygous dominant or heterozygous.

42 Multiple Alleles Genes may have more than two alleles.

43 Multiple alleles: Some genes have more than two variations that exist, although we still only inherit 2 Example: Human blood types Three alleles: IA IB i Genotype Phenotype IAIA A IAi IBIB B IBi IAIB AB ii





48 Multiple genes code for a trait each with 2 alleles
Polygenic – Multiple genes code for a trait each with 2 alleles Examples in humans: Skin Color Eye Color Height Why so many possibilities??? SKIN PIGMENTATION

49 Dihybrid cross: A cross that focuses on possibilities of inheriting two traits - two genes, 4 alleles Black fur is dominant to brown fur Short fur is dominant to long fur What is the genotype of a guinea pig that is heterozygous for both black and short fur?

50 Dihybrid cross: Parent phenotypes: BbSs x BbSs Figure out the possible gametes: Then set up punnett square

51 Dihybrid cross: BS Bs bS bs


53 Di-hybrid Cross Generalization
Laws of probability indicate a 9:3:3:1 phenotypic ratio of F2 offspring resulting in the following: 9/16 of the offspring are dominant for both traits 3/16 of the offspring are dominant for one trait and recessive for the other trait 3/16 of the offspring are dominant and recessive opposite of the previous proportions; and 1/16 of the offspring are recessive for both traits.

54 Linkage and Gene Maps When genes are one separate chromosomes, they independently assort. If on the same chromosome, they will rarely separate and be inherited together (gene linkage) Actually it is the chromosomes that assort independently, not the genes. Mendel was just lucky with the genes he was looking at!

55 Crossing over in meiosis often separates linked genes.
The distance between the two genes on the same chromosome are from each other affects the frequency of separation from each other during crossing-over. Further Apart Closer together 

56 The frequency of crossing over between genes is actually an indicator of how far apart different genes are located from each other on the same chromosome. Use the frequency rates to make gene maps that show relative locations of genes with respect to each other.


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