MENDELIAN GENETICS How does Genetics connect with DNA
- Slides: 25
MENDELIAN GENETICS
How does Genetics connect with DNA? • DNA RNA Amino Acids Protein • Genes Traits • Thus, different variations of each trait, known as alleles, arise when mutations in DNA = different Amino Acid sequences, which = different proteins, which = different traits.
Mendel and His Beloved Peas • Garden peas are: • Self-pollinating • Easy to experimentally cross-pollinate • Clear traits—pure purple, pure white, etc.
Trait: any single feature of an organism Traits That Mendel Studied ALLELES
Gregor Mendel: Classical Genetics • Principle of Dominance • Principle of Segregation • Principle of Independent Assortment • Video clip: Alleles & Genes
Principle of Dominance • Some alleles are dominant, others are recessive. • Dominant alleles “overpower” the recessive. • EXCEPTIONS: • Incomplete Dominance • Codominance
What Mendel Noticed: • P Generation (“Parent”) • F 1 Generation (“First Filial”) (Kids) • “Short” trait disappears… Whoa! • F 2 Generation (“Second Filial”) (Grandkids) • …then reappears!
Did You Catch That? • Where did that short plant (trait) come from?
Recessive Traits “Hide” Behind Dominant Traits • Sexual organisms have two of alleles for each trait, one allele on each chromosome of a homologous pair. • One homologue of each pair is passed on to offspring by each parent. (p 265)
Recessive Traits “Hide” Behind Dominant Traits PLANT HEIGHT • Different forms of the same trait are called alleles • What TRAIT is being studied in this experiment? “Tall” … and … “Short” • What are the TWO ALLELES (forms) of the trait being studied?
Principle of Segregation • Alleles are separate from one another; each gamete only carries a single copy of each gene • EXCEPTION: • Nondisjuntion
Mendel proposed that “Factors” segregate (separate) from pairs to be passed on to offspring, one from each parent! (p 265 -266)
Homologous chromosomes split up in Anaphase II so that only one allele of each trait gets passed on in your gametes!
Principle of Independent Assortment • Genes for different traits segregate independently of one another during the formation of gametes (sperm/egg) • EXCEPTION: • When genes for different traits are on the same chromosome they are likely to travel together and are called “linked” traits.
This principle assumes that each trait is carried on a different chromosome, thus alleles for each trait sort into gametes (sperm/egg) independently, regardless of which alleles for other traits a gamete will receive.
The pair of alleles you have (for any trait) is called your GENOTYPE Example Trait: Nose Shape (Let us pretend that round nose is dominant to pointy nose) (usually, letters are used to represent alleles, upper case for dominant) • Alleles: ___ (dominant), ___ (recessive) n N • Genotypes: ____, ____ NN Nn nn “Homozygous Dominant” (Purebred) “Heterozygous” (hybrid or carrier) “Homozygous Recessive” (Purebred)
Another Example: • What’s the TRAIT? • What are the ALLELES? • Which is dominant? PP pp Pp
Remember: Only one of each allele is passed on from each parent! • What is Mom’s genotype? Heterozygous • What is Dad’s genotype? Ova (either) Heterozygous GERM CELL Pp Pp Sperm (either) GERM CELL
Let’s Look At the Offspring Probabilities Ova (either) • What if this egg meets this sperm? Sperm (either) What if this egg meets this sperm?
This Is Called A Punnett Square • Punnett squares allow us to predict probabilities about offspring
What percentages does this Punnett square predict? • How many 75% (3/4) Purple? ______ • How many White? ______ 25% (1/4) • How many homozygous dominant? 25% ___(1/4) • How many heterozygous? ______ 50% (2/4) • How many homozygous recessive? ___ 25% (1/4) 25% 25%
What is the probability that this couple will have a baby with the “a” disease? • Healthy allelle = A • Disease allele = a 25% (1/4)
What is the probability that this couple will have a baby who is a CARRIER for the “a” disease? • Healthy allelle = A • Disease allele = a 50% (2/4) A CARRIER is a heterozygote (he or she can “pass on” the trait but does not exhibit it)
Your Turn! (For disease “A”): What if a homozygous dominant man marries a carrier woman? AA Aa ____ X ____ Dad Mom A a A AA Aa Offspring Genotype: - HD (AA) = ___% 50 - Het (Aa)= ___% 50 - HR (aa)= ___% 0 Offspring Phenotype: - Healthy* = ___% 100 - Disease = ___% 0 - *(Healthy) Carrier = 50 _____%
One More Time! (For disease “A”): What if a carrier man marries a woman with the disease? Aa ____ X aa ____ Dad Mom a a A Aa Aa a aa aa Offspring Genotype: 0 - HD (AA) = ___% 50 - Het (Aa)= ___% 50 - HR (aa)= ___% Offspring Phenotype: - Healthy* = 50 ___% 50 - Disease = ___% - *(Healthy) Carrier = 50 _____%
- Family resemblance test
- Is baldness a sex linked trait
- Section 11-4 meiosis answer key
- Heterozygous b blood type
- Codominant biology definition
- Section 11-3 exploring mendelian genetics
- Chapter 10 section 2 mendelian genetics
- Mendel was a
- 11-3 exploring mendelian genetics
- Section 11-3 exploring mendelian genetics
- Extending mendelian genetics answer key
- Extension of mendelian genetics
- Section 11-3 exploring mendelian genetics answer key
- Xnxn horse
- Chapter 7 extending mendelian genetics vocabulary practice
- Pleiotropism definition
- Co doninance
- Mendelian theory of inheritance
- Pedigree miscarriage symbol
- Mendel's theory of particulate inheritance __________.
- Mendelian genetics vocab
- Incomplete vs codominance
- Color blindness punnett square
- Heredity concept map
- Chapter 7 extending mendelian genetics vocabulary practice
- 11-3 exploring mendelian genetics