Two copies of genes found on homologues have same function but DNA sequence may differ May have two different alleles of same gene Genotype is the particular genetic or allele makeup of an individual Phenotype is the observable or measurable feature of an individual Autosome all the chromosomes except for the sex chromosomes Chapter 11 Single Gene Inheritance and Meiosis Cystic Fibrosis CF Genetic disease Caused by a single gene mutation Change in nucleotide sequence of DNA Creates a new mutant allele Allele of the CFTR gene CFTR gene codes transmembrane regulator protein Moves ions in and out of cells How are genes inherited Genes provide instructions for making proteins Physically transmitted 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 Sexual Reproduction Combination of maternal and paternal alleles Join during fertilization Determines genotype and contributes to phenotype Requires special sex cells sperm egg Gametes reproductive cells that carry one copy of each chromosome Haploid Meiosis Special cell division needed to reduce from diploid to haploid Meiosis generates genetically unique haploid gametes Haploid sperm fertilizes haploid egg The result is a diploid zygote Zygote divides by mitosis into and embryo Meiosis Two separate divisions steps Meiosis I Separates homologous chromosomes Each daughter cells is haploid Each chromosome still has two sister chromatids Meiosis II Separates sister chromatids Four haploid daughter cells Develop into egg or sperm Meiosis and genetic diversity No two gametes are identical Due to recombination and independent assortment Recombination when maternal and paternal chromosomes pair and physically exchange DNA segments Independent Assortment alleles of different genes are distributed independently of one another Cystic Fibrosis CFTR protein is distorted Abnormally thick mucus builds up in the lungs Inheriting cystic fibrosis People with normal phenotypes can still pass CF allele to offspring People with CF will not necessarily have offspring with CF Why Cystic fibrosis is recessive Allele different version of the same gene 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 letter a Dominant allele designated by upper case letter A Genotype recessive and dominant Heterozygote two different alleles Aa Phenotype is normal Individual is a carrier Homozygote two identical alleles Homozygous dominant AA Phenotype is normal Homozygous recessive aa Phenotype is CF mutant Punnett square A diagram to determine the probabilities of offspring having particular genotypes Based on genotypes of the parents Matches up all possible gametes Multiple genes can contribute to phenotypes CF severity influenced by genes on other chromosomes For example TGF 1 influences immune response to infection Can follow alleles through gamete formation using Punnett square Predict likelihood of offspring being homozygous recessive for disease Treating CF therapies Understanding how modifier genes contribute to the disease may point the way to even more For example Kalydeco is effective at restoring function to the malfunctioning CFTR channel Summary parents to offspring Genes which code for proteins are the units of inheritance physically passed down from An organism s physical traits constitute its phenotype its genes constitute 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 mutations that change Alleles may be dominant or recessive Dominant alleles can mask the effects of recessive alleles the nucleotide sequence of a gene which can be hidden Meiosis is a type of cell division that produces genetically distinct haploid sperm and egg A Punnett square can help predict a child s genotype and phenotype Chapter 12 Complex Inheritance What determines biological sex Sex chromosomes produced by gonads Ovaries in females testes in males Androgens testosterone estrogen Males produce higher levels of testosterone Females produce higher levels of estrogen In a fetus sex hormones shape development of sexual anatomy Depends on the set of chromosomes fetus receives from parents Humans have 23 pairs of chromosomes In the absence of a Y chromosome a fetus will develop into a female 22 pair are autosomes 1 pair are sex chromosomes Females are XX Males are XY Sons inherit their Y chromosome from father and X chromosome from mother Daughters inherit one X chromosome from mother and one from father SRY gene on Y chromosome signals testes to develop Testes produce testosterone Genetic hormonal anatomical and behavioral aspects to sex Gene located on either side of the sex chromosomes daughters and sons don t share the same Sex linked inheritance probability of inheriting X linked trait A phenotype that is determines by allele on an X chromosome Recessive X linked trait normal copy on one X chromosome masks the recessive disease allele on the other X chromosome For example Duchenne muscular dystrophy DMD A male has a single X chromosome so he will show the effects of any recessive alleles located on his X chromosome Mother passes one of her X chromosomes to her children Father passes his only X chromosome to his daughters and his only Y chromosome to his sons Boys have only one X chromosome and have a higher probability of inheriting X linked diseases than girls Use a pedigree to follow inheritance patterns Pedigree visual representation of the occurrence of phenotypes across generations Y chromosome Y chromosome analysis Very small and contains few genes Study ancestry and identify paternity Sons inherit Y chromosomes from fathers Compare DNA sequences Compare short tandem repeats STRs on Y chromosome Incomplete dominance There are two versions of the genes that specify hair texture But three phenotypes curly straight wavy A form of inheritance in which heterozygotes have a phenotype that is intermediate between homozygous dominant and homozygous recessive Codominance Transfused blood must be compatible in ways that are determined by genetics Both maternal and paternal alleles contribute equally and separately to the phenotype Blood type Three blood group alleles A B O Genotypes OO AO BO AB AA BB Blood