Presentation on theme: "Chapter 10 Genetics: Mendel and Beyond Biology 101 Tri-County Technical College Pendleton, SC."— Presentation transcript:
Chapter 10 Genetics: Mendel and Beyond Biology 101 Tri-County Technical College Pendleton, SC
It’s a character trait A character is a feature such as flower color Best described as a gene A trait is a particular form of a character, such as white flowers Best described as an allele A heritable character trait is one that is passed from parent to offspring Before Mendel, blending was model of choice…and it was logical to a point
Law of Segregation Mendel and it’s all about flowers and sex In sexually reproducing organisms, an individual possesses 2 “factors” for each trait One came from mommy and one from daddy When that individual makes gametes, those “factors” (alleles) will separate (segregate) from each other and wind up in different gametes **Gamete receives only ONE member of the pair of alleles
Defining Definitions Genotype is genetic constitution of the organism It’s what in the genes Phenotype is the physical expression of the genotype It’s what one sees—phenotype is the expression of genotype Dominant means always expressed (in the phenotype) Only one allele needed for its expression DOES NOT MEAN “THE BEST TO HAVE”
Definitions, cont. Recessive means “covered”, “hidden”, or “masked” by presence of dominant allele Recessive allele only expressed when present in pairs Homozygous means “same” or two copies of same allele Can be homozygous dominant or homozygous recessive TT or tt, respectively
Definitions, cont. Heterozygous means “different” or “other” Two different alleles of the “trait” (gene/allele) in question (Tt) Monohybrid means differing in only ONE trait tall or short; yellow or green, etc. Dihybrid means differing in TWO traits tall and yellow; short and green
Monohybrid Cross P = parental generation F 1 = first filial generation (first generation of hybrid) F 2 = second filial generation (second generation of a hybrid) Punnett square is an application that allows prediction of probability of genotypes/ phenotypes from a genetic cross
Test Cross Test cross is dated concept that still serves useful purpose Estes and the field of corn Defined as mating an individual of unknown genotype with an individual homozygous recessive for the trait Figure the Punnett square for this one…you will see it again!!
Law of Independent Assortment In dihybrid crosses, parental traits appear in new combinations of 2 of the phenotypic classes such new combinations called recombinant phenotypes Alleles of different genes assort independently of one another during gamete formation In other words, T does not always stay with Y and vice versa Law of Independent Assortment NOT as universal as law of segregation
Independent Assortment, cont. Applies to genes on separate chromosomes but not necessarily to those that lie on same chromosome Simply states that chromosomes segregate independently during formation of gametes as do any two genes (alleles) on separate chromosome pairs
Dihybrid Crosses Review: dihybrid means two contrasting traits TTYY crosses with ttyy Do the Punnett square and look for 9 genotypes and 4 phenotypes Be sure and remember the phenotypic ratio…you will see it again and again!!!
Incomplete Dominance When heterozygous phenotype is intermediate, gene is said to be governed by incomplete dominance/lack of dominance Looks like blending to be sure Time for a Wally World story…Yeah!!!! Red and white snapdragon cross produces all pink offspring All F 1 to self-fertilize and predict F 2 Black rooster and white hen = all gray chicks Red bull and white cow = all roan calves
To dominate…or Not Complete dominance results when single allele produces enough protein to give maximum phenotypic response Incomplete dominance results when heterozygotes show intermediate phenotype Codominance results when two alleles at locus produce two different phenotypes that both appear in heterozygoes Means both are fully expressed Best example is ABO blood grouping
ABO Blood Grouping Blood type determined by proteins on surface of RBCs Protein coded for by info in DNA Alleles are I A and I B There are six genotypes and four phenotypes This is ABO only, we will discuss Rh factor This one always gets me into trouble Chalk talk time on ABO and Rh typing
Linkage Association between markers (genes/alleles) on same chromosome such that they do NOT show random assortment and seldom recombine Closer the markers, lower frequency of recombination Closer they are together, more likely they are to STAY together MAP units
Determining Sex Sex (gender) determined by sex chromosomes (23 rd pair) Females are XX and males are Xy AFAWK, only thing on y chromosome is SRY (male-determining) gene and gene for hairy ears Nature was not overly kind to males Implications of XX and Xy
Sex-linked Disorders Defined as being “tied” to X sex chromosome Sex-linked disorders affect males more One mutant recessive allele leads to red- green colorblindness, muscular dystrophy, and hemophilia Human mutations inherited as sex-linked dominant must LESS common than recessives
Sex-linked, cont. Dominants appear in every generation and individuals carrying harmful mutation (even as heterozygotes) often fail to survive and/or reproduce Chalk talk time on hemophilia and/or color blindness
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