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Biology Unit Four C – Chromosomes and Phenotype Mrs. Pearson’s First Semester Biology *For those watching by recording, watch for questions on the slides throughout the presentation. Email me the answers to the questions within two days of the lesson being presented in order to receive credit for watching the recording. 7.1 Chromosomes and Phenotype Lesson Objectives • Discuss nature of sex linked traits • Discuss factors affecting the expression of phenotypes 7.1 Chromosomes and Phenotype Getting Rave Reviews… • • • • • • • Phenotype Genotype Recessive Dominant Heterozygote Homozygote Allele 7.1 Chromosomes and Phenotype Word of the Day! • Autosomal • Any chromosome that is NOT one for determining whether the organism is male or female. 7.1 Chromosomes and Phenotype Two copies of each autosomal gene affect phenotype – How do we know this? • Mendel studied autosomal gene traits, like hair texture. • If a gene is not autosomal, what is it? 7.1 Chromosomes and Phenotype • Mendel’s rules of inheritance apply to autosomal genetic disorders. – A heterozygote for a recessive disorder is a carrier. Why? – Disorders caused by dominant alleles are uncommon. (dominant) **Those watching by recording, include in your email why it is uncommon to have a dominant allele that causes a disorder. 7.1 Chromosomes and Phenotype Males and females can differ in sex-linked traits. • Genes on sex chromosomes are called sex-linked genes. – Y chromosome genes in mammals are responsible for male characteristics. – X chromosome genes in mammals affect many traits – not just female traits. 7.1 Chromosomes and Phenotype • Male mammals have an XY genotype. – All of a male’s sexlinked genes are expressed – Why? – Males have no second copies of sex-linked genes. **Those watching by recording, include in your email why all of a male’s sex linked genes are expressed. 7.1 Chromosomes and Phenotype • Female mammals have an XX genotype. – Expression of sex-linked genes is similar to autosomal genes in females – why? – X chromosome inactivation randomly “turns off” one X chromosome. 7.2 Complex Patterns of Inheritance Phenotype can depend on interactions of alleles. • In incomplete dominance, neither allele is completely dominant nor completely recessive – what might a heterozygous individual look like? – Heterozygous phenotype is intermediate between the two homozygous phenotypes 7.2 Complex Patterns of Inheritance • Codominant alleles will both be completely expressed. What might that look like? – Codominant alleles are neither dominant nor recessive. – The ABO blood types result from codominant alleles. • Many genes have more than two alleles. 7.2 Complex Patterns of Inheritance Many genes may interact to produce one trait. • Polygenic traits are produced by two or more genes. Order of dominance: brown > green > blue. 7.2 Complex Patterns of Inheritance The environment interacts with genotype – think of a way the environment may affect phenotype. • Phenotype is a combination of genotype and environment. • The sex of sea turtles depends on both genes and the environment • Height is an example of a phenotype strongly affected by the environment. **Those watching by recording, include in your email why height is strongly affected by environment. 7.2 Complex Patterns of Inheritance Review • • • • Two copies of each autosomal gene affect phenotype Males and females can differ in sex-linked traits\ Phenotype can depend on interactions of alleles In incomplete dominance, neither allele is completely dominant nor completely recessive • Codominant alleles will both be completely expressed • Many genes may interact to produce one trait • The environment interacts with genotype 7.1 Chromosomes and Phenotype Questions?