exam 3 BIOL 1333 - 002
Popular in DISCOVERING BIOLOGY: MOLECULES, CELLS AND DISEASE
BIOL 1333 - 002
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This 10 page Study Guide was uploaded by shal on Monday November 2, 2015. The Study Guide belongs to BIOL 1333 - 002 at University of Texas at Arlington taught by Claudia P Marquez in Summer 2015. Since its upload, it has received 34 views. For similar materials see DISCOVERING BIOLOGY: MOLECULES, CELLS AND DISEASE in Biology at University of Texas at Arlington.
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Date Created: 11/02/15
11/2/14 Chapter 11 Single-‐Gene Inheritance and Meiosis Driving Ques▯ons 1. How does the organiza▯on of chromosomes, genes, and their alleles contribute to human traits? 2. How does meiosis produce gametes? 3. Why do diﬀerent traits have diﬀerent inheritance pa▯erns? 4. What are some prac▯cal applica▯ons of understanding the gene▯c basis of human disease? Cys▯c ﬁbrosis (CF) • Gene▯c disease • Caused by a single gene muta▯on – change in nucleo▯de sequence of DNA – creates a new mutant allele • Allele of the CFTR gene 1 11/2/14 Cys▯c ﬁbrosis (CF) • CFTR gene codes transmembrane regulator protein • Moves ions in and out of cells How are genes inherited? • Genes provide instruc▯ons for making proteins • Physically transmi▯ed from parent to oﬀspring • Two copies of each chromosome (and each gene) in diploid organisms – homologous chromosomes – one from each parent passed to oﬀspring Humans are diploid organisms 2 11/2/14 Humans are diploid organisms • Two copies of genes found on homologues have same func▯on but DNA sequence may diﬀer • may have two diﬀerent alleles of same gene Humans are diploid organisms • Genotype is the par▯cular gene▯c or allele makeup of an individual • Phenotype is the observable or measurable features of an individual Sexual reproduc▯on • Combina▯on of maternal and paternal alleles • Join during fer▯liza▯on • Determines genotype and contributes to phenotype 3 11/2/14 Sexual reproduc▯on • Requires special sex cells: sperm, egg • Gametes: reproduc▯ve cells that carry one copy of each chromosome – haploid • Special cell division needed to reduce from diploid to haploid – meiosis Sexual reproduc▯on Meiosis generates gene▯cally unique haploid gametes Sexual reproduc▯on • Haploid sperm fer▯lizes haploid egg • The result is a diploid zygote • Zygote divides by mitosis into an embryo 4 11/2/14 Meiosis • Two separate divisions steps • Meiosis I – separates homologous chromosomes – each daughter cell is haploid – each chromosome s▯ll has two sister chroma▯ds Meiosis • Meiosis II – separates sister chroma▯ds – four haploid daughter cells – develop into egg or sperm Meiosis and gene▯c diversity • No two gametes are iden▯cal • Due to recombina▯on and independent assortment 5 11/2/14 Meiosis and gene▯c diversity • Recombina▯on: when maternal and paternal chromosomes pair and physically exchange DNA segments Meiosis and gene▯c diversity • Independent assortment; alleles of diﬀerent genes are distributed independently of one another Cys▯c ﬁbrosis • CFTR protein is distorted. • Abnormally thick mucus builds up in the lungs 6 11/2/14 Inheri▯ng cys▯c ﬁbrosis • People with normal phenotypes can s▯ll pass CF allele to oﬀspring • People with CF will not necessarily have oﬀspring with CF • Why? Cys▯c ﬁbrosis is recessive • CF is caused by a recessive allele – an allele that aﬀects phenotype only if the organism has two copies of that allele – hidden by normal or dominant allele • recessive allele designated by a lower-‐case le▯er (a) • dominant allele designated by upper-‐case le▯er (A) Genotype: recessive and dominant • Heterozygote: two diﬀerent alleles (Aa) – phenotype is normal – individual is a carrier • Homozygote: two iden▯cal alleles • Homozygous dominant (AA) – phenotype is normal • Homozygous recessive (aa) – phenotype is CF (mutant) 7 11/2/14 Genotype: recessive and dominant • Punne▯ square • A diagram to determine the probabili▯es of oﬀspring having par▯cular genotypes • Based on genotypes of the parents • Matches up all possible gametes Inheritance of recessive trait Inheritance of dominant trait 8 11/2/14 Dominant and recessive traits Mul▯ple genes can contribute to phenotypes • CF severity inﬂuenced by genes on other chromosomes • For example: TGFβ1 inﬂuences immune response to infec▯on Mul▯ple genes can contribute to phenotypes • Can follow alleles through gamete forma▯on using Punne▯ square • Predict likelihood of oﬀspring being homozygous recessive for disease 9 11/2/14 Trea▯ng CF • Understanding how “modiﬁer” genes contribute to the disease may point the way to even more therapies • For example, Kalydeco is eﬀec▯ve at restoring func▯on to the malfunc▯oning CFTR channel Summary • Genes, which code for proteins, are the units of inheritance, physically passed down from parents to oﬀspring. • An organism’s physical traits cons▯tute its phenotype; its genes cons▯tute its genotype. • Diploid organisms have two copies of each chromosome in their cells. • Diﬀerent versions of the same gene are called alleles. Alleles arise from muta▯ons that change the nucleo▯de sequence of a gene. • Alleles may be dominant or recessive. Dominant alleles can mask the eﬀects of recessive alleles, which can be hidden. • Meiosis is a type of cell division that produces gene▯cally dis▯nct, haploid sperm and egg. • A Punne▯ square can help predict a child’s genotype and phenotype when the pa▯ern of inheritance, dominant or recessive, is known. 10
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