Introduction to Genetics

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Myron Benson
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1 Introduction to Genetics

2 Why do children look like their parents? The answer is genetics Genetics is the scientific study of heredity Heredity is the passing down of traits from parents to offspring (by genes)

3 Chromosomes, DNA, and Genes Chromosomes are made of DNA Each strand of DNA contains genes Each gene contains the code, or instructions, for one trait you will display A trait is a specific characteristic (such as having dimples, or being able to roll your tongue) So, chromosomes = DNA = genes = code = traits

4 Gregor Mendel Australian monk in the 1860s Studied different traits of garden pea plants Discovered the basic laws of genetics Called the Father of Genetics

5 Gregor Mendel Used scientific method and mathematics to systematically study many generations of pea plants (over 29,000!) 1 st person to successfully predict how traits are passed from one generation to the next Trait a characteristic (what an organism looks like or how an organism behaves)

6 Pea Plants Pea plants worked well because they grow quickly Mendel identified several traits of pea plants

7 Dominant vs. Recessive Mendel discovered that one trait would be dominant over the other. Dominant trait = stronger. The other trait would be recessive. Recessive trait = weaker. If a pea plant had the genes for both traits, then the plant would display only the dominant trait Example: one trait for yellow seeds (dominant), one trait for green seeds (recessive) the pea plant would have yellow seeds

8 Dominant vs. Recessive The only time a pea plant would display a recessive trait, is when both of its genes coded for the recessive trait Example: both genes code for green seeds (recessive) the pea plant will have green seeds

9 Genes vs. Alleles GENE: section of DNA that determines a trait ALLELE: particular form of a trait Represented by letters Dominant: capital letter Recessive: lowercase letter Example: yellow seeds vs. green seeds Dominant: yellow seeds (Y) Recessive: green seeds (y) Y y

10 Combinations of Alleles For each trait, we have two alleles We get one allele from each parent 3 possibilities YY homozygous dominant yellow seeds Yy heterozygous yellow seeds yy homozygous recessive green seeds Homo = same Y y Hetero = different/other

11 Genotype & Phenotype Genotype the specific combination of genes that an organism has YY Yy yy Phenotype the physical appearance that the organism will display yellow seeds green seeds Y y

12 Let s Practice!

13 Height: Dominant: Tall (T) Recessive: Short (t) Alleles: T, t Homozygous dominant Heterozygous Homozygous recessive Genotype Phenotype

14 Height: Dominant: Tall (T) Recessive: Short (t) Alleles: T, t Genotype Phenotype Homozygous dominant TT tall Heterozygous Tt tall Homozygous recessive tt short

15 Seed shape: Round is dominant (R) Wrinkled is recessive (r) Alleles: R, r Homozygous dominant Heterozygous Homozygous recessive Genotype Phenotype

16 Seed shape: Round is dominant (R) Wrinkled is recessive (r) Alleles: R, r Genotype Phenotype Homozygous dominant RR round Heterozygous Rr round Homozygous recessive rr wrinkled

17 Seed Coat Color: Green is dominant (G) White is recessive (g) Alleles: G, g Homozygous dominant Heterozygous Homozygous recessive Genotype Phenotype

18 Seed Coat Color: Green is dominant (G) White is recessive (g) Alleles: G, g Genotype Phenotype Homozygous dominant GG green Heterozygous Gg green Homozygous recessive gg white

19 Hidden Genes Genes can skip generations if the parents carry the allele for the recessive gene Example: Both parents are Yy (heterozygous) for seed color. Yellow is dominant, so both parents will be yellow But both parents are also carrying the recessive allele for green (y) If both parents pass down the y allele, the offspring will be yy and have green seeds Y y

20 You Try! How can two tall (T) pea plants have a short (t) offspring? T What genotype will the offspring be? What phenotype will the offspring be? t What genotype must BOTH parents be? What phenotype will they be?

21 You Try! How can two tall (T) pea plants have a short (t) offspring? T What genotype will the offspring be? tt What phenotype will the offspring be? short What genotype must BOTH parents be? Tt (they are tall but each one needs a short allele to pass to offspring) t What phenotype will they be? tall

22 You Try! G = green pod, g = yellow pod. If an offspring has a yellow pod, what genotype does it have? G What TWO possible genotypes can each parent have? g What color(s) could the parents be?

23 You Try! G = green pod, g = yellow pod. If an offspring has a yellow pod, what genotype does it have? gg What TWO possible genotypes can each parent have? Gg or gg (as long as each parent has at least ONE g to give) G g What color(s) could the parents be? Green (Gg) or yellow (gg)

24 You Try! R= round seeds, r = wrinkled seeds. An offspring has round seeds. R Mother is rr. What is her phenotype? What genotype will the offspring have? r What phenotype MUST the father be? What 2 genotypes can the father be?

You Try! R= round seeds, r = wrinkled seeds. An offspring has round seeds. Mother is rr. What is her phenotype? wrinkled What genotype will the offspring have?

25 You Try! R= round seeds, r = wrinkled seeds. An offspring has round seeds. Mother is rr. What is her phenotype? wrinkled What genotype will the offspring have? Rr (because mother can only give an r, but offspring needs an R to be round) What phenotype MUST the father be? Round (must have at least one R) R r What 2 genotypes can the father be? RR or Rr

26 Great Job! Make sure you know the following: Relationship between chromosomes, DNA, genes, and traits Who Gregor Mendel was and why he s so important Vocabulary: Trait Gene Allele Dominant Recessive Genotype Phenotype Homozygous dominant Heterozygous Homozygous recessive How recessive traits can be hidden and skip generations

Genetics. The study of genes and the inheritance of traits

Genetics. The study of genes and the inheritance of traits Genetics The study of genes and the inheritance of traits THE STUDENTS WILL: Explain how traits are inherited Identify the role of Gregor Mendel in the History of Genetics Use a Punnett Square to predict