Genes and Heredity

Life Science - Middle School

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earlobe freckles Widow’s peak eyebrow shape www.newpathlearning.com © Copyright NewPath Learning. All Rights Reserved. 94-4635 Genes and Heredity Heredity Heredity is the passing of traits or characteristics from one generation to the next. When an egg and a sperm unite, a copy of each parent’s genes is incorporated into the resulting embryo. Humans have about 100,000 genes spread over 46 chromosomes. Half of these chromosomes come from the person’s mother, and the other half come from the person’s father. A Look at Traits The laws of dominance determine whether a child will display the trait coded for by a gene inherited from its father or its mother. Some genes, called dominant genes, express themselves when only one copy is present. Other genes, called recessive genes, express themselves only when two copies are present. Scientists use capital letters to designate dominant genes and lowercase letters to represent recessive ones. An individual with two recessive genes or two dominant genes for a trait is said to be homozygous for that trait. An individual with one dominant gene and one recessive gene is said to be heterozygous. Making a Pedigree A pedigree is a diagram showing the transmission of a genetic trait through several generations of a family. It provides clues to the kinds of traits that may be passed on to future offspring. A pedigree is also useful for determining the genotype of an individual, as well as predicting the genotypes of future generations. In a pedigree, each individual is represented by an Arabic number, while each generation is represented by a Roman numeral. Squares represent males and circles represent females. A shaded box indicates an individual who displays the characteristic being studied. The genetic makeup of an individual is known as a genotype, while the observable physical characteristics that result from an individual’s genotype is known as a phenotype. Genetic Traits Trait Dominant Gene Recessive Gene chromosome pair gene A B c D e F G h i J a b C d E f g H I j Human Karyotype 1 2 3 6 7 8 9 10 11 12 13 14 19 20 21 22 XX (female) XY (male) 15 16 17 18 4 5 or DNA gene Inheritance of Attached Earlobes Generation I Generation II Father Ee ee Mother ee child 1 Ee child 2 Ee child 3 tongue rolling roller nonroller Widow’s peak present absent shape of earlobe free attached freckles present absent shape of eyebrows bushy fine mid-digital hair present absent
freckles eyebrow shape DNA gene www.newpathlearning.com © Copyright NewPath Learning. All Rights Reserved. 94-4635 Genes and Heredity Heredity _________________ is the passing of traits or characteristics from one generation to the next. When an __________ and a ___________ unite, a copy of each parent’s genes is incorporated into the resulting _________. Humans have about 100,000 _____________ spread over ______ chromosomes. Half of these chromosomes come from the person’s _____________ , and the other half come from the person’s _____________ . A Look at Traits The __________ ____ __________________ determine whether a child will display the trait coded for by a gene inherited from its father or its mother. Some genes, called ____________ _________, express themselves when only one copy is present. Other genes, called ____________ _________, express themselves only when two copies are present. Scientists use capital letters to designate _____________ genes and lowercase letters to represent ______________ ones. An individual with two recessive genes for a trait is said to be _____________ for that trait. An individual with one dominant gene and one recessive gene is said to be _____________ . Making a Pedigree A ________________ is a diagram showing the transmission of a genetic trait through several generations of a family. It provides clues to the kinds of traits that may be passed on to future offspring. A pedigree is also useful for determining the _____________ of an individual, as well as predicting the genotypes of future generations. In a pedigree, each individual is represented by an ____________ ____________ , while each generation is represented by a ____________ ____________ . ____________ represent males and ____________ represent females. A ________________ _________ indicates an individual who displays the characteristic being studied. The genetic makeup of an individual is known as a _____________ , while the observable physical characteristics that result from an individual’s genotype is known as a _____________ . Genetic Traits Trait Dominant Gene Recessive Gene Key Vocabulary Terms chromosome heterozygous dominant gene homozygous genes Laws of dominance genetic trait pedigree genotype phenotype heredity recessive gene Human Karyotype 1 2 3 6 7 8 9 10 11 12 13 14 19 20 21 22 XX (female) XY (male) 15 16 17 18 4 5 or Inheritance of Attached Earlobes Father Ee ee Mother ee child 1 Ee child 2 Ee child 3 roller nonroller present absent free attached present absent bushy fine present absent \|xiBAHBDy01749tz]